The Cleveland Cavaliers have the best record in the NBA and the best player in the world on their roster. Of course this was the exact same scenario for the Cavs last season, and they ultimately lost to Orlando in the conference finals.

General manager Danny Ferry bolstered his team with additions big (Shaquille O’Neal and Antawn Jamison) and small (Anthony Parker, Jamario Moon) and found improvement from within in young forward J.J. Hickson.

Noted Celtic killer Anderson Varejao had the best season of his career, Mo Williams continued to shoot over 40 percent from 3-point range, effectively ending the necessity for Daniel Gibson to get playing time, and Delonte West re-emerged as a key third guard.

Then, there is LeBron James, who has shattered the best player in the league argument and seems poised to truly rule the world if he can deliver a championship to his hometown team before engaging in the most frenzied free agent courtship the league has ever known.

Ah, but the Celtics have other ideas. They have the distinction of owning two wins against Cleveland this season, an achievement shared by only Orlando and Denver.

Those wins did come with mitigating circumstances attached: The first was on opening day, which may as well have been another lifetime ago. The second was on Easter Sunday when the Cavs were without O’Neal and Varejao and mounted a furious second-half rally in a game that turned into what Boston coach Doc Rivers called a “must win” by the time it was over.

For their part, the Cavs handled the Celtics at home in March, turning a relatively close game into a blowout and in the ultimate indignity, reversing a double-digit deficit into a 20-point romp at the Garden. Considering the litany of embarrassing Celtics losses at home it’s hard to place where that one ranks, but it’s definitely in the top five.

Still, there’s a notion that this might be the right time for the Celtics to play Cleveland. It’s earlier in the playoffs, and they will have the benefit of a few days rest between series, so they should be fresher.

“Listen, if we want to win it, [we’ve] got to play them all anyway,” Rivers said after the Celtics got past Miami. “So, you know, why not now? We’re there. We’ll be waiting. We’ll be ready.”

James is also dealing with some kind of elbow injury, the extent of which is not really known, although it seems to have originated several weeks ago. James said he had an MRI and an X-ray on Monday and he seemed limited in Game 5, electing to shoot a free throw left-handed down the stretch.

James, who can hang with Paul Pierce when it comes to milking injuries, told reporters there was nothing to worry about. But we won’t know how much it’s bothering him until Saturday. Assuming James is as healthy as he needs to be, here’s a look at the matchups that will define the series.

PAUL PIERCE VS. LEBRON JAMES

Memories are still fresh of Pierce’s epic battle with James in the 2008 conference semifinals. It was one of the finest moments of Pierce’s career, and gave him a signature moment to define his Boston legacy.

And yet, in this game history is for suckers and storytellers. Pierce is two years older and James is two years deeper into his prime. P.J. Brown’s not walking through that door and Wally Szczerbiak is long gone. These are different times.

That said, Pierce is one of the few players in the league who can even contemplate getting physical with James.

After a series in which Pierce’s defensive responsibility was Quentin Richardson, whose only skills seemed to be annoying Pierce and shooting 3’s, this will be a whole other test. Like Dwyane Wade, James is the epicenter of the Cleveland attack. His numbers (29.7 points, 7.3 rebounds, 8.6 assists) are obvious enough, and his advanced metrics make him look even better.

Everything revolves around him, but unlike Wade his supporting cast is much better.

If James has a weakness, it is as a 3-point shooter. He took more 3’s than anyone on the Cavs and made only 33 percent of them. That isn’t to say that he isn’t capable of putting on insane shooting exhibitions (witness the Chicago series where he made 13-of-24), but if you want him to shoot from anywhere it’s from behind the arc.

James averaged better than 36 points a game against the Celtics this season, but he shot less than 30 percent from 3-point range (8-for-27) and he also shot more 3’s against them any other team, which suggests the Celtics have read the scouting report.

Defending James will also put a significant amount of heat on the Celtics big men, who will have to deal with pick and pops via Jamison and pick and rolls via the energetic Varejao. Again, James has teammates who can actually hurt you if you give them too much space and for all his shot attempts, he’s also an unselfish passer.

For his part, Pierce has moved beyond trying to make this a one-on-one thing with James. His focus when they have played has been on the defensive end. Pierce is playing some of his best basketball of the season right now, but this will be the toughest challenge he will face.

THE BACKCOURTS

The Cavs guards define the word “serviceable.” Mo Williams takes and makes a lot of 3’s, Anthony Parker plays defense and is a spot-up 3-point shooter off rotations and kick outs and Delonte West does a little bit of everything. What the Cavs don’t have is a true floor leader in the backcourt, but with James they don’t really need one.

If the Celtics are going to pull the upset this is where they have to dominate, and Rajon Rondo is the key. The Cavs don’t really have anyone who can stay with him, but if form holds they won’t try. They effectively used the free safety defense against Rondo in the past, completely ignoring him on the perimeter and letting his defender roam, but this season Rondo was able to average 15 points and 10 assists in their four games against the Cavs.

While making jumpers is an obvious deterrent against that strategy, the most important thing for Rondo is to simply keep attacking, either with the ball or with movement when it’s out of his hands. If he allows himself to be invisible then Cleveland is more than happy to oblige him.

The Celtics are also at their best when they rebound and outlet to Rondo for the fast break. If he can get out in the open floor there’s no gimmick defense in the world that can stop him.

The Celtics also need for Ray Allen to continue his torrid shooting. Finally freed from the responsibilities of guarding Wade, Allen can channel the majority of his effort into running off screens and firing jumpers. Williams is certainly capable of getting hot and Parker is a pro’s pro, but this is a matchup the Celtics need to win every night.

THE FRONTCOURTS

There are two games going on up here. The first involves O’Neal and Kendrick Perkins, two heavyweight behemoths battling for space down low. The other may decide the series.

When the Cavs go small (although it’s hard to define any lineup with James in it as small), they are at their best. With James at the four, flanked by either Varejao or Hickson, they can be absolutely devastating. Throw in Jamison’s ability to step out and make jumpers and it creates tons of empty floor space for James to fill with drives and Varejao to crash the glass.

The Cavs embarrassed the Celtics in their January matchup at the Garden when Varejao outworked and outhustled the Celtics big men.

The longer the Cavs play with a conventional lineup, the better it will be for Boston. Garnett will take Jamison and Perkins will play Shaq. Those aren’t easy matchups, but they’re fairly straightforward.

It’s when Mike Brown calls on Varejao and Hickson that chaos ensues and the Celtics have to do a much better job dealing with it in this series than they did in the regular season.

THE BENCHES

Tony Allen played a crucial role in the Miami series as the designated Wade stopper. He not only defended Wade as well as could be expected, he also handled the backup point guard duties without embarrassment and was active around the basket on the offensive end. Allen will have his moments in this series. He will help on James, and it’s worth remembering the two go into some excited conversation the last time the two teams played.

But from the reserves’ perspective, this series belongs to Glen Davis. He must match Varejao’s energy with his own. Every loose ball must become a personal battle and he must remember why he is on the floor.

“He is so talented and his IQ is ridiculous,” Rivers said after Game 5. “But, you know, he lets up at times. He starts thinking about what he’s done well, instead of just keep playing. He has proven over the long haul, though, that in big games he tends to play well. He did it in college and he’s done it here.”

In addition to Varejao, Hickson and West the Cavs also have used athletic freak Jamario Moon in spots and his length and athleticism can cause problems. Beyond Allen and Davis, the Celtics veteran reserves Michael Finley and Rasheed Wallace didn’t show much in the Miami series. Finley remains trusted. Wallace remains an enigma.

It wouldn’t be a total shock if Nate Robinson had some kind of role in this series. The Cavs guards are small and if Rivers feels like he needs instant offense he showed in the Miami series that he won’t hesitate to call on Robinson.

THE INTANGIBLES

For the first time in their three-year run, the Celtics are healthy and an underdog. The players may not see it this way, but they are playing with house money at this point. Very few people realistically expect them to win this series.

The Cavaliers, on the other hand, are facing a mountain of pressure. James will be a free agent and it remains to be seen if a championship, or a lack thereof, will influence his decision one way or the other, but it will be a dominant storyline.

Regardless of whether this is James’ swan song, Cleveland is built to win now. Ferry made big, bold moves and the ownership didn’t skimp on the extras like Parker and Moon.

The Cavs did not handle pressure very well last season against Orlando, and if this series gets tight, it will be interesting to see how they react. Will Brown stick with Williams if his shot goes haywire? Will he sit O’Neal if need be? Observers have been waiting all season to learn the answers to those questions.

The James shoulder injury is the ultimate X-factor is this series, but assuming he is good to go the Cavs will have no excuse if their run ends here.

The Cavs should win the series, but if the Celtics can continue their improved defensive play, limit Varejao on the glass and decisively win the backcourt matchup it could be far more interesting then what everyone predicted when the playoffs started.