But manager Terry Francona cautioned not to read that as any kind of lack of confidence in Delcarmen, who posted a 3.27 ERA in a staff-leading 73 outings.
"That can change in a hurry," said Francona, who got 1 2/3 innings out of Delcarmen in Game 3 when starter Josh Beckett lasted just five innings. "With the way [the Angels'] lineup is set up, it's hard not to go to Masterson in certain situations. Manny Delcarmen, before this is all said and done, he will have pitched very meaningful innings. I'd be willing to guarantee that."
What makes Masterson such a great fit against the Angels is that their lineup, at times, has as many as five righties stacked up in a row.
Masterson, a sinkerballer, is particularly tough on righties, who hit just .196 against him during the season.
Though he did walk in a run in the seventh inning of Game 2, he bounced back with a critical strikeout.
The rookie continues to look anything but overwhelmed. At midseason, the Red Sox opted to move him from the rotation to the bullpen, feeling it could fill a need on the team. After a short apprenticeship in the Minor Leagues, Masterson quickly became a key to the Boston bullpen during the second half.
"We've been impressed," Francona said. "I think we were pretty open about the fact that that's how we envisioned this working. And it's worked out really well."
In Sunday night's 5-4 loss in 12 innings in Game 3, Masterson allowed one hit over 1 1/3 frames of relief.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.