In 16 games for the Red Sox, Mortensen is 1-1 with a 1.72 ERA. He has held opponents to a .178 batting average over his 31 1/3 innings.
"Gosh, Clay has pitched in a lot of different situations to a lot of different types of hitters and has been consistently good," Red Sox manager Bobby Valentine said. "His breaking stuff is different than anyone we have on our staff. It's always good to have different looks and his look is really different and I think it's just as effective against left-handers as it is against right-handers."
Mortensen can also start, though the Red Sox haven't asked him to perform in that role yet.
"Remember, we were thinking about having him start in the Minor Leagues and then there was a necessity to put him back in the bullpen," Valentine said. "So I guess there's some curiosity and, again, I'm not always of the opinion that you build championship teams by taking good pitchers and always making them starters. I think championship teams are built with bullpens also and he can be a very valuable person."