BOSTON -- Because of Daisuke Matsuzaka’s struggles this season, the Red Sox’ contingency plan has worked more often than not.

 That fallback plan relies heavily on the right shoulder of Justin Masterson. The reliever/starter/reliever has served different roles during his young major league career, but in 2009 he’s become Matsuzaka’s shadow.

 On two occasions this season, Masterson has been asked to clean up the mess. and he’s done a solid job.

The first came in Oakland on April 14 when Dice-K worked only one inning and allowed five runs on five hits on 43 pitches. Masterson followed and pitched four scoreless innings and allowed only two hits as the Sox battled back and eventually won, 6-5 in 12 innings.

The second time occurred Friday night at Fenway when Masterson began to warm in the top of the first inning as Matsuzaka imploded. He allowed only two runs, but it could have been a lot worse as he loaded the bases only to get out of the jam with some defensive help.

Masterson sat back down in the bullpen. He was up again in the fifth as Matsuzaka began to struggle again. The Japanese import was given the hook after facing two batters in the fifth and manager Terry Francona handed the ball over to Masterson.

The slick right-hander worked the next 2 1/3 innings, allowing one unearned run on one hit.

It’s become almost a given Masterson is the go-to guy, especially when Matsuzaka struggles.

"I don’t think you ever want to be warming up in the first," said Masterson. "Dice tried to get back on track, and the bullpen tried to keep it close."

Matsuzaka has yet to work six full innings this season - although he’s reached the sixth six times. That’s the spot in the middle innings where Masterson would prefer to work.

"Several times this year, it’s been a little earlier than that," he said. "He’s pitched not too terrible at times, maybe an inning gets away and today wasn’t the highest for him. He’s battling like anyone else. Once he figures out what he’s got, hopefully he relaxes and goes out there and throws."

No matter what role the Red Sox have needed Masterson he’s been there to bail the club out, and his presence hasn’t gone unnoticed.

 "He’s been a valuable part of our staff - period," said captain and batterymate Jason Varitek. "Both as a starter, reliever, short guy and long guy and he’s able to do a lot of different things. . . He has abilities and that’s the big thing. He has the abilities to throw strikes with a couple of different pitches, so that’s huge. He’ll continue to gain more experience. He’s getting a feel for himself still. He’s doing a good job at it."

Pitching versatility has become second nature for Masterson during his big league career.

"I feel good. I’ve been pretty comfortable in whatever role it’s been," he said.