Fourth-inning homers by Piazza and Alfonzo enabled New York to take a 3-1 cushion into the fifth. But the Reds loaded the bases with one out against starter Pedro Astacio, and Austin Kearns hit a blast that caromed high off the left field wall.
Perez trapped it against the fence, then showed the ball to the umpires, none of whom was close to the play because the crew was down to three after plate umpire Bill Miller left with a sprained right ankle. Perez threw back to the infield, doubling Todd Walker off second base to end the inning.
Alomar provided insurance with a solo shot in the seventh, and the lead proved enough for Astacio (10-3), who gave up two runs and six hits over seven innings with four walks and seven strikeouts to win his fourth straight start.
Mark Guthrie and Scott Strickland combined to get through the eighth and Armando Benitez struck out the side in the ninth for his 22nd save.
Reds knuckleballer Jared Fernandez (1-1) served up two of the Mets' homers and surrendered three runs and six hits in five innings, striking out three without a walk.