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10/02/08 3:30 AM ET

Master's degree for rookie righty

Backed by his defense, young reliever shuts down Halos

ANAHEIM -- What does a rookie pitcher think when he's thrust into the eighth inning of a one-run playoff game with the meat of the Angels' order due up?

"I try not to think," Red Sox reliever Justin Masterson said with a smile after his club posted a 4-1 victory in Game 1 of its American League Division Series contest vs. the Angels. "Does that make sense?"

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Sure does. And by shutting off his brain, Masterson was able to shut down the Angels in the eighth inning of Wednesday's Game 1 -- with quite an assist from his supporting cast on the defensive end.

A wild eighth inning in which the Red Sox held on to the slimmest of leads was both a credit to their defensive acumen and to the steely nerves of their 23-year-old setup man.

"I always say I'm as good as my defense," said Masterson, who entered the frame with the Sox clinging to a one-run lead. "Guys made some great plays to get out of that inning."

The first such play came when leadoff man Mark Teixeira hit a fly ball to center, and Jacoby Ellsbury charged in on the ball and made a sensational diving catch for the inning's first out.

After Vladimir Guerrero reached on a single, Torii Hunter lifted one into shallow right, just over the head of first baseman Kevin Youkilis. When Guerrero mistakenly streaked toward third on the play, Youkilis' heads-up decision to pick up the ball and come up firing to third paid off, as he easily nabbed Guerrero.

"That was a great play," Masterson said. "You see him running and yell, 'Throw!' I'm glad he did run."

The threat of Masterson giving up a run was all but muted by that point. He got Howie Kendrick to ground into a fielder's choice to end the inning, and the Red Sox added a pair of insurance runs in the ninth to put the game away.

Masterson, by virtue of his 2.36 ERA since July 23, knew he might be presented with the opportunity to have a prominent relief role in this game.

But that doesn't mean he wasn't nervous.

"You're definitely nervous out there," Masterson said, "but you try to bottle it up to use it."

Expect the Red Sox to keep using the fresh-faced Masterson in plenty of prominent spots this postseason, though Manny Delcarmen and left-hander Hideki Okajima will also share the setup duties.

"It was great to get out there," Masterson said. "I got the opportunity today. Probably, in the next game, it might be another guy or it might be me again. We have a lot of guys who can get the job done."

Anthony Castrovince is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.