CLEARWATER, Fla. - Jonathan Papelbon’s conversion from closer to starter didn’t last long.

Papelbon is heading back to Boston’s bullpen to fill a major void, though he isn’t doing it because an injury to Mike Timlin left the Red Sox without a closer.

“I haven’t been sleeping well because there’s been that feeling deep down in my heart that I wanted to close,” Papelbon said after the Phillies and Red Sox played to a 4-4 tie in 10 innings on Thursday.

Papelbon is coming off a sensational rookie season in which he had 35 saves and an 0.92 ERA. But he was shut down with a month to go because of shoulder problems, and the Red Sox had planned to use him in the rotation to keep him on a more regular schedule.

The Red Sox needed a reliable closer because the 41-year-old Timlin has a strained side muscle and isn’t going to be ready to start the season.

Papelbon made the decision to tell manager Terry Francona how he felt about returning to his closer’s role earlier this week after consulting with his family and speaking to catcher Jason Varitek.

“He’s unique,” Francona said. “He’s at the top of the list of relievers in baseball. He impacts the game like no other. I’m thrilled we have a young guy that feels enthusiastic about doing a job.”

Papelbon allowed one run and two hits in three innings against Philadelphia. Karim Garcia’s RBI single in the seventh off Papelbon tied the game at 4.

Julian Tavarez will take over as Boston’s fifth starter behind an impressive staff that includes Curt Schilling, Josh Beckett, Daisuke Matsuzaka and Tim Wakefield.

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Papelbon opened last season with 20 consecutive saves after taking over for injured closer Keith Foulke. The 26-year-old right-hander blew six of his last 21 chances, and missed the final month with a shoulder injury. Overall, Papelbon’s rookie year was one for the ages.

Among pitchers who threw more than 50 innings, his ERA was the eighth lowest in major league history and his .167 opponents batting average tied him for the major league record Pedro Martinez set in 2000, when the former Boston ace won the Cy Young Award.

Papelbon’s injury led the club to switch him back to the starting rotation because the routine of having to be prepared to pitch every day — and being in games two or three consecutive nights — might have caused some stress. Papelbon pitched almost exclusively as a starter in the minors, but worked out of the bullpen at Mississippi State and was selected as a closer in the fourth round of the 2003 amateur entry draft.

Papelbon pitched 68 1-3 innings in 59 appearances last year. He was 4-2 with 75 strikeouts and only 13 walks.

“This is something I want to do for the rest of my career,” he said. “It has nothing to do with Timlin’s health or us not having a closer or my shoulder. I broke into the league as a closer. They drafted me as a closer. In college, I learned to pitch in the bullpen. It’s where my heart is.”

Papelbon isn’t concerned about re-injuring his shoulder as a reliever.

“If I do what I’m supposed to do, get checked out day in and day out, there’s no reason why I can’t pitch in October,” he said.

Papelbon’s role model is Mariano Rivera, who has been a dominant closer for several years while helping the rival New York Yankees win four World Series titles.

“Hopefully I can do what Rivera has done for the Yankees,” he said.

Francona probably won’t overuse Papelbon and likely won’t send him out for two-inning saves often.

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“He’ll be checked, monitored and I’ll tell him he’s not pitching certain days and he’s going to do strengthening exercises,” Francona said. “I’d never put a ballclub’s best interest ahead of the health of a player.”

General manager Theo Epstein said decisions can’t be based only on a player’s desire, but Papelbon showed last year how much he helped the team as a closer.

“A player is not going to succeed in a starting role if he feels inside he’s a closer and has demonstrated he’s one of the best in the world,” Epstein said in a conference call. “He’s committed to doing this and doing it extremely well for the next decade.”

Finding a closer was “the key issue” coming into camp, he said, “but it wasn’t one that we were tremendously concerned about.”

Before Papelbon entered against the Phillies, Wakefield pitched six innings, allowing three runs — two earned — and eight hits. Phillies starter Jamie Moyer gave up four runs and five hits in five innings, striking out seven, and Jon Lieber tossed two scoreless innings in his first outing since being sent to the bullpen a day earlier.

Chase Utley hit a two-run homer off Wakefield in the first inning.

Wily Mo Pena hit a solo shot in the second for the Red Sox, and Kevin Youkilis drove a three-run homer over the left-field wall and beyond the tiki bar behind the stands in the third.