It was one of the most dizzying and decisive offseason days in recent Red Sox memory.

It started with news that the trade of Mike Lowell to the Rangers for catcher Max Ramirez was in jeopardy due to concerns that Lowell might require thumb surgery. Ordinarily, such a development would be monumental. Yet by the end of Monday, it bordered on an afterthought.

That was because the Sox spun heads by bringing John Lackey to Boston for a physical, en route to reportedly coming to terms on a five-year deal described as being worth between $82.5 million and $85 million.

The move represented a significant surprise, given that the Sox had defined a resolution of their situation in left field as the team’s top offseason priority. All indications pointed toward the Sox either re-signing Bay or pursuing fellow free agent outfielder Matt Holliday.

Instead, two days after Bay’s agent, Joe Urbon, said that his client was “moving on” from the Sox’ most recent offer, the Sox likewise elected to move on from Bay, throwing their resources into the longtime anchor of the Angels’ pitching staff.

That seemed a likely harbinger of the end of Bay’s career as Red Sox left fielder. And indeed, that outcome arrived with news that the Sox signed outfielder Mike Cameron to a two-year deal (pending a physical) for what FoxSports.com reported as $15.5 million, almost surely spelling the end of Bay’s time in Boston.

The turn of events was sudden and seismic, changing the shape of the 2010 Red Sox significantly. Here is a look at what the arrival of Lackey and Cameron in Boston means to both the Red Sox and several other parties:

JOHN LACKEY

The Red Sox entered 2009 expecting to have a stacked rotation. That design faltered.

Josh Beckett and Jon Lester were both dominant over the course of the season. But behind them, the Sox were riddled with issues of health (Tim Wakefield, whose first All-Star year ended sadly after the first half), ill conditioning (Daisuke Matsuzaka, who made himself irrelevant for the first five months of the year after showing up out of shape in spring training) and underperformance (Brad Penny and John Smoltz, both of whom were disappointments in their brief Boston tenures).

Rather than taking a flier on another buy-low pitcher, the Sox went after the best available starter on the free agent market. The 31-year-old has been one of the best bets for solid performance in the majors.

Lackey is one of three pitchers in the majors — joining Carlos Zambrano and Johan Santana — with at least 162 innings and a sub-4.00 ERA in each of the past five years. His numbers (102-71, 3.81 ERA, 7.2 strikeouts and 2.6 walks per nine innings) in his career with the Angels are strikingly similar to Beckett’s (106-68, 3.79, 8.5 strikeouts and 2.7 walks per nine innings).

He does not shy from the spotlight, as demonstrated when he won Game 7 of the 2002 World Series in his rookie year, and again when he overpowered the Sox in Game 1 of the 2009 ALDS, tossing 7-1/3 shutout innings. He has a career 3.12 ERA in 78 playoff innings. The Angels insist that he has been a top-of-the-rotation pitcher.

“John is obviously one of the top starting pitchers in our league,” Halos skipper Mike Scioscia said at the Winter Meetings last week. “I don’t know if there’s many pitchers that are out there, certainly this year there aren’t many pitchers that are out there, that would be available, that are going to combine the depth that he can pitch in an individual game with his ability to go out there and compete in any situation in any ballpark. That’s what makes — that’s why we want him back in an Angels uniform and that’s also why other teams are interested in John.

“John could handle playing anywhere. He could handle playing in New York, Chicago, Los Angeles, any area. This guy is as focused as any pitcher I’ve seen with the ability to just forget about the environment he’s pitching in and focus in on that catcher and what he needs to do in a certain situation against a hitter and execute it. A lot of guys have the focus, they just aren’t able to do it. … John is a special talent.”

Assuming the deal goes through, Lackey gives the Sox a rotation that features three pitchers — Lackey, Lester and Beckett — who would front most rotations in the majors. The appeal for the Sox is apparent.

Red Sox manager Terry Francona expressed his admiration for Lackey earlier this offseason on the Dale & Holley show. At the same time, the Sox skipper acknowledged the risk associated with pursuing a top-of-the-rotation pitcher for a long-term deal, particularly given that Lackey is at an age when pitchers typically become less healthy, not more.

“John Lackey is one of the best. Every year, there’s a couple of guys that seem like they can sway the fortunes of an organization. He’s that type of pitcher,” Francona said. “Now, to get that type of pitcher, you’re going to have to make quite a commitment. That’s something that makes our organization a little bit uneasy. It doesn’t mean a guy can’t come in and help you win. If there’s an injury along the way, that can set your organization back quite a bit. There’s a lot to think about besides just the year 2010. You’re possibly talking about 2015. That’s a lot of years.

“I probably do [consider him an ace],” he continued. “He’s missed a little bit of time, but when he’s out there, I think their team feels it’s going to win. He can match up against Beckett, Lester. He can go head-to-head with the better guys in the league and hold his own.”

Lackey looks the part of an innings-eating horse, and for most of his career, he had been one. He made no fewer than 32 starts every year from 2003-07 before being limited to 24 starts in 2008 and 27 starts in 2009 by a triceps injury in 2008 and elbow inflammation this year.

Nonetheless, he was strong down the stretch this year, recording a 2.89 ERA over his last seven regular-season starts and a 2.29 ERA in three playoff starts, including his dominant outing in the ALDS against the Red Sox.

Lackey is 2-5 with a 5.75 ERA in nine career regular-season starts in Boston, though he has also made some excellent starts in Fenway Park, most notably when he carried a no-hitter into the ninth inning in July 2008, and when he allowed two runs in seven innings in a no-decision in Game 4 of the ALDS. Of Lackey’s six most recent regular-season starts in Fenway Park (dating to the 2005 season), he has four quality starts.

He has been one of the best pitchers in the American League for much of this decade. If Lackey can remain relatively healthy as a member of the Red Sox, he will give Boston a rotation that may well be the most dominant in the majors.

That is a giant and expensive “if.” Free agent pitchers typically represent terrible risks, and those signed to deals of four or more years almost never perform up to their contracts. The Sox have never spent as much on a free agent pitcher (in either total dollars or average annual value) as they will spend on Lackey, nor have they ever committed the kind of years to a pitcher that Lackey will get. (Daisuke Matsuzaka, whom the Sox signed for six years and $52 million, was not a free agent when acquired through the posting process from Japan's Nippon Professional Baseball League.)

Even so, the cost for Lackey is less steep than would have been the acquisition of a pitcher such as Roy Halladay, for whom the Phillies will have to cough up both money and prospects. If Lackey flames out, the cost to the Sox was purely financial, rather than representing a drain on the team’s minor league system.

MIKE CAMERON

With the signing of Lackey, it would have been virtually impossible for any club — save the Yankees — to add Jason Bay to the mix while remaining under budget. And so, after the Sox reportedly agreed to terms with the pitcher, they made an aggressive move to sign a player who, in the batter’s box, profiles as Jason Bay Lite.

The Sox signed Cameron for two years. FoxSports.com reported the deal as being for $15.5 million — a bit less than one year of Bay might have cost. 

Cameron (who has a career average of .250 with a .340 OBP and .448 slugging average, with marks of .250/.342/.452 in 2009 for the Brewers) strikes out a lot (about once a game). He takes his walks. He sees plenty of pitches. He has significant pop. And, ultimately, the team that has him knows almost exactly what it will get.

“I would say [Cameron] is one of the most consistent outfielders in the game,” said former Padres GM Kevin Towers, for whom Cameron played in 2006-07. “His numbers, regardess of being in Milwaukee, San Diego, the Mets, Seattle, you can almost bank on somewhere between 18 and 25 home runs, somewhere between 70 and 90 RBIs. He’s going to hit around .250, .260, with an OPS close to .800 every year.”

“He’s remarkably consistent,” agreed Rays (and former Red Sox) outfielder Gabe Kapler, who played with Cameron in Milwaukee. “You look at his numbers, you can predict the kind of numbers at the beginning of the year that Mike Cameron is going to be at the end of the year. You know what his power numbers are going to be. They’re there every year.”

As a hitter, Cameron is a shadow of Bay, though he does have legitimate offensive skill. Cameron, who averaged 3.96 pitches per plate appearance in 2009, is nearly as exhausting an opponent for pitchers to face as was Bay, who saw 3.99 pitches per at-bat last year. Though Cameron’s stolen bases dropped sharply in 2009 (at the age of 36), he is still considered a better baserunner than Bay.

But, perhaps most significantly, Cameron is a tremendous defensive outfielder. Whereas Bay’s strongest advocates described his defense as average (and some viewed him in much less flattering terms), Cameron — even at age 36 — still is viewed as one of the elite outfielders in the game.

Whether Cameron joins the Sox as a left fielder (a position at which he has played just three career games, none since 2000) or remains in center field — the position from which he has won three Gold Gloves — he should contribute to the ongoing transformation of a Sox defense that ranked among the worst in the majors in ’09.

"Everyone I've talked to believes [Cameron] to be one of the top defensive center fielders in the league," said former Sox outfielder Gabe Kapler, who played with Cameron in Milwaukee in 2008. "He's going to make the Red Sox defense a whole lot better."

“He’s still a solid defender. He plays a great center field and should be even a better corner outfielder,” added Towers. “I think Mike can play any of the outfield positions well. It’s always nice to have your outfield with a couple different center fielders out there.”

Still, while Cameron will help the Sox' run prevention, he clearly is not Bay's offensive equal. Few are — Bay has been one of the most productive outfield regulars in the game over recent seasons.

But regardless of how one viewed Bay's defense in left field — and assessments among talent evaluators range from average to slightly below average to well below average — the Sox will offset some of that drop-off with a clear improvement in their defense. With Cameron and Marco Scutaro now signed as free agents, the Sox now have gone from one of the worst defensive teams in the majors to a potentially above-average one, with the opportunity to become elite in that category should the team complete the trade of Mike Lowell to Texas and either sign Adrian Beltre or move Kevin Youkilis from first to third, with Casey Kotchman playing first base next year.

Between Cameron, Lackey and Scutaro, the Sox will hope that the sum of the new contributors will make them better than they were with Bay.

The deal also has implications for several other players, among them:

JASON BAY

It is now fairly obvious that Bay’s Boston career is over. The Sox used the money that would have gone to him — and then some — to acquire a pitcher rather than an outfielder.

(It is worth noting that Lackey’s deal is far larger than the one that the Sox had on the table for Bay. It is also worth mentioning that a deal such as the one that Lackey will sign with the Sox almost surely would have gotten a deal done with Bay. So, in a sense, the Sox concluded that they were better off with Lackey than Bay.)

The Sox are set with four primary outfielders (Cameron, Jacoby Ellsbury, J.D. Drew and Jeremy Hermida) for 2010. Just as Bay’s agent, Joe Urbon, said that Bay was ready to move on from the Sox, so, too, did the Sox prove ready to move on from Bay.

Now, the Bay market will undergo some redefinition, in light of both the Red Sox’ move and the reported three-way blockbuster that sent Roy Halladay to the Phillies and Cliff Lee to the Mariners.

The Mets, obviously, remain the team with the most aggressive known offer on the table, having extended to four years and between $60 million and $65 million. The Mariners are believed by baseball sources to remain in pursuit of more pitching, though it is worth noting that Lee’s relatively modest 2010 salary ($9 million) would not prevent Seattle from offering a deal to Bay.

The Angels — who wanted to retain Lackey, and who were also exploring a deal for Halladay — missed out on the top three pitchers who will move this offseason. They had been earmarking cash for pitching (and other needs); it is conceivable that they could either pursue another top starter via trade, or that they could change course and use their resources to pursue a player for whom they have publicly pronounced their admiration in Bay.

The Giants and Cardinals could also come into play, particularly if St. Louis decides that Bay is a more affordable alternative to its own free agent, Matt Holliday. And, finally, the Boston Herald is reporting that the Yankees have at least contacted Bay’s representatives to express some interest; New York does have an opening in left field, with Hideki Matsui now gone to the Angels and Johnny Damon a free agent.

CLAY BUCHHOLZ/JOSH BECKETT/DAISUKE MATSUZAKA

Every other pitcher under Red Sox control becomes somewhat more expendable with Lackey in the mix, since the club has found a top-of-the-rotation option who would make all of them, in theory, more expendable. This offers twofold flexibility.

First, it becomes somewhat easier for the team to deal any of them, most likely Buchholz, who is the most sought-after pitcher on the market. Buchholz will not be eligible for free agency until after the 2014 season; he could be a front-of-the-rotation pitcher for the next five years.

Now, in Lackey, the Sox have a pitcher who is at least in theory ready to assume such a role. Moreover, with Casey Kelly committed to pitching, the Sox have another hurler on the horizon who is viewed as an up-and-coming top-of-the-rotation pitcher.

For Beckett, the Sox now find themselves negotiating his extension from a position of strength. The team need not view itself as being in a position where it must get a deal done with the right-hander. Instead, the Sox will enjoy a position of some comfort when it comes to retaining Beckett beyond 2010, knowing that if he goes, they have already signed his potential replacement; if they can retain him, then they have as formidable a rotation as any for the long haul.

ADRIAN GONZALEZ/MIDDLE-OF-THE-ORDER HITTERS

The Padres — including GM Jed Hoyer and manager Bud Black — have said that they have no intentions of dealing slugging first baseman Adrian Gonzalez before the start of the season. However, if/when the Padres do put the 40-homer masher on the market, the Sox will be picking up the phone. And with Buchholz potentially available as the centerpiece for a deal, it becomes a lot easier for the Sox to make a deal for either San Diego’s superstar or another middle-of-the-order bat.

JACOBY ELLSBURY

The world is rich with possibilities for Ellsbury. With Cameron — a three-time Gold Glover in center field — in tow, Ellsbury could remain in center, a position where the Sox believe that he will eventually become an above-average defender.

He could be moved to left, where his lateral range is already tremendous and his current difficulties reading the ball in and out would be masked. Such an alignment would be reminiscent of when the Sox had Ellsbury flanking Coco Crisp at times in 2007 (when Manny Ramirez was injured) and 2008 (when Ramirez served as DH while David Ortiz was out).

Ellsbury has started 48 career games in left. The Sox enjoy a healthy .625 winning percentage in those games (30-18), having offset the loss of a bat (usually Ramirez or Ortiz) with better outfield run prevention.

ADRIAN BELTRE AND CASEY KOTCHMAN

The Sox' commitment to improved defense and run prevention is now obvious. Already, the team has positioned itself for a big defensive upgrade thanks to the arrivals of Cameron, Scutaro and Lackey.

The logical next step might be the acquisition of Beltre, a spectacular defender, to replace Lowell at third base (assuming that the deal with Texas goes through, a matter that will take at least some time to resolve given that the Rangers will examine Lowell in person to determine whether he needs surgery on his thumb). Yet, the Sox may well be nearly at their payroll limit for 2010, given their commitments of roughly $100 million to two players on Monday.

If that's the case, then the team may well turn to Kotchman, who also is considered one of the better defensive first basemen in the majors. Kotchman would permit Kevin Youkilis to cross the diamond to third base, giving the Sox a much stronger infield than the one they featured in 2009, even if not the nearly seamless one that could have been in play with Beltre.