Perez made his first appearance right away, in Saturday's 5-4 loss to the Twins at Miller Park. He entered the game in the top of the seventh with runners on first and second and one out in a 2-2 tie. He walked the bases loaded before hitting Ben Revere to allow a run.
"He's up taking a flight at five in the morning to get here," manager Ron Roenicke said. "And of course it ends up being [that] with the game on the line, we've got to bring him in."
The next day, Perez lasted just two-thirds of an inning, striking out a batter but also walking one and surrendering a run. In a 5-4 loss to the Giants on Monday, he pitched a full inning and once again struggled with his control, walking two batters but also striking out two.
Perez turned in his best performance in Tuesday's 6-4 loss to San Francisco, pitching one scoreless inning and striking out two.
In all, Perez -- who before making eight appearances with the Phillies last season hadn't pitched in the Majors since 2007 -- has a 6.75 ERA with five strikeouts and five walks in 2 2/3 innings.
Despite the up-and-down results, Roenicke thinks the 33-year-old left-hander could be a valuable asset to a bullpen that has been called upon often recently.
"[I had to] put him in a couple of tough situations that I wish I wouldn't have had to," Roenicke said. "But he's made some good pitches, and he's struggled with some."