ARLINGTON, Texas – Five years ago today, a closer was born.

The Red Sox entered the 2006 season trying to gauge whether 2004 postseason hero Keith Foulke, after struggling through and then missing much of 2005 with bad knees, could regain his form. They received their answer in spring training and then the first game of the regular season against the Rangers, when Foulke had nothing while giving up a run on two hits in a garbage-time inning of the Sox’ 7-3 win.

And so, as the Sox prepared for their third game of the season at the Ballpark in Arlington on April 5, 2006, manager Terry Francona made a bold gambit. If the opportunity presented itself, he would entrust a save situation to rookie Jonathan Papelbon.

“I think we knew what we thought Pap could be or we wouldn’t have done it,” Francona recalled this weekend. “If there’s a veteran, I’m going to err on the side of caution. But I think we knew what we had with Pap.”

Papelbon had made a strong impression after a mid-year call-up in 2005. He had a 2.65 ERA and struck out a batter an inning that year, mostly as a setup man. Then, against the White Sox in the Division Series, he delivered four overpowering shutout innings in the playoffs.

The 25-year-old, the Sox concluded, had the lightning arm, the explosive fastball and the fearlessness to take command of the ninth if Foulke faltered.

And so, prior to that game against the Rangers, Francona had three conversations. First, in deference to what Foulke had done for the Sox, the manager talked to the veteran.

“We had a guy who had put us on his shoulders in the playoffs, so I think you have to be respectful of what you say,” recalled Francona. “But I had talked to Foulkie enough that he knew where things were.

“I remember I had said something to Foulkie that night. I said, ‘I just want to give you a head’s up. If we get into this situation, I’m going to go to Pap.’”

Foulke was not under any delusions. He knew that he had never been the same since the 102-inning workload he delivered for the Sox in 2004 — a 2.17 ERA in 83 regular season innings, followed by a 1.42 ERA in 19 more playoff innings, including an incredible run in which he threw 100 pitches over a three-day, three-game stretch in the ALCS against the Yankees.

He was still trying to work his way back to health at that stage, and didn’t try to fight Francona when the news was delivered. Foulke would never again record a save for the Sox, and he had just one more save in the remaining 74 contests of his career.

Francona’s next conversation was not planned. He was making his usual rounds to touch base with his players in the outfield during batting practice. As he chatted with Curt Schilling, the manager revealed the planned change.

“I was telling him, ‘I’m thinking about going to Pap,’” Francona recalled. “Schill goes, ‘You better be right. You sure you know what you’re doing?’”

But Francona had no doubt about how he wanted to proceed. And so, there was a final conversation with the person who was about to move from middle relief to a game-ending phenomenon.

“About 30 minutes before game time, Tito just called me into the office and said he thought long and hard about, starting the season off, who was going to close, and we decided on you,” Papelbon remembered. “We want to give you the chance to start shutting the door in the ninth. Just go out there and do the best you can.”

Immediately, the excitement level for Papelbon ratcheted up as he got ready for the game. But he remained focused. He had been a closer in college at Mississippi State and understood the process that he needed to follow to prepare for the game.

“I knew, kind of, what to expect,” said Papelbon. “I had closed at the Triple-A level and I had closed in college. It wasn’t going into the game blind. I just remember that day doing what I knew to do.”

In Josh Beckett’s Red Sox debut, the Rangers scored a first-inning run and no more. The Sox finally plated a pair of runs in the seventh inning, putting Beckett in position for the win.

Setup man Mike Timlin, who had closed for the Sox at the end of 2005, survived a rocky eighth inning, with Mark Teixeira getting gunned down at the plate when trying to score from second on a one-out single. And so, with the Sox clinging to a 2-1 lead over the Rangers in the bottom of the ninth, the bullpen door swung open and Papelbon started sprinting to the mound, electricity jolting through him.

“I remember it pretty vividly,” Papelbon said this weekend. “I’ve gotten some good [adrenaline rushes] — Yankee Stadium, World Series, Fenway Park. But that first one is definitely, it was the same feel but yet different meaning. Same feel, same adrenaline, but just a different meaning.

“I remember thinking to myself, after it was all said and done, ‘Wow, for my first save opportunity in the big leagues, this was as intense as they came, pretty big one right out of the gate, day one.’ I just remember thinking, ‘Wow, pretty intense.’ I enjoyed it.”

So did the Sox. Asked to preserve the one-run lead against Rod Barajas, Laynce Nix and Brad Wilkerson, Papelbon was geared up and ready.

“I remember I had great stuff that day,” he said. “I had an overpowering fastball that night.”

His save was ruthless — a five-pitch strikeout of Barajas, a first-pitch pop-up to short by Nix and a five-pitch strikeout of Wilkerson. That Papelbon responded in such overpowering fashion to a one-run game — this was no three-run gimme — was telling.

The Sox had thrown Papelbon into the fire. He had not wilted.

He came in throwing about 97. He haad all that adrenaline. That was a fun one,” said Francona. “That’s when he’s good. I think that’s what we learned — that’s when he excels. He wants to compete.”

Still, the Sox avoided naming Papelbon their permanent closer for some time in 2006. They continued to talk about shifting the right-hander back to the rotation, and continued to suggest that the door remained open for Foulke to reclaim his role if his stuff returned.

But the idea of using anyone but Papelbon as the closer that year quickly became little beyond a theoretical exercise. Papelbon was so exceptional in 2006 — saving 35 games, punching out 75 and walking just 13 in 68 1/3 innings — that he never gave the Sox a choice in the matter.

From the time that he recorded that first save, Papelbon was in love with the role. It was a hand-in-glove fit.

“I wouldn’t say [closing] is what I was born to do,” said Papelbon, “but in that same sense, this is what I dreamed of doing.”

In 2006, he was a rookie who was simply “trying to find a niche on the club.” But by the end of that year, he knew how he wanted to spend the rest of his career.

And so, even after the Sox decided that he should be moved back to the rotation for the 2007 campaign following his season-ending shoulder subluxation in 2006, he couldn’t embrace the decision. After drifting through spring training in 2007, he made the decision late in camp — at a time when the Sox had yet to identify a closer — to approach the team and make his preference known.

“I felt at that point in time that this is my career, that I have to voice my opinion. It’s nobody else’s career,” said Papelbon. “Yeah, they’re the boss, and they may want me to do something else, but I still have to tell them what I would like to do, and if they agree to it, great, and if they don’t, I still have to voice my opinion and tell them what I would like to do. That way, I was living without any regrets.”

The Sox welcomed Papelbon back to the role, and he has owned it since. In five years in his role, he has 188 saves, most in Red Sox history, and most in the American League in that time. Even with last year’s down year, he has had one of the most dominant five-year runs of any closer in big league history.

Papelbon has moved beyond that wide-eyed beginning of his closing career. He has experienced the game’s highest pinnacles, as the pitcher on the mound as the Sox clinched the World Series, and he has in the last year experienced struggles as well, in 2009 when he absorbed the loss that eliminated the Sox from the playoffs, and in 2010 when — despite 37 saves and more than a strikeout an inning — he experienced his lengthiest stretches of vulnerability.

Yet while he is at a very different stage of his career now than he was in the first days of the 2006 season, it takes little for him to summon that initial experience as the Red Sox closer five years ago. Anytime he returns to the home of the Rangers — as he did during the season’s opening weekend — the memory of his first big league save remains fresh.

“Even when I came here this year,” said Papelbon, “this park will always trigger that first time.”

That is with good reason, as it was a change of role that changed both the course of Papelbon’s career and the shape of the Red Sox.