The Reds hit three homers in all as they pulled within 6½ games of the NL Central leaders.
Tucker Barnhart led off the fifth with his first career homer. Todd Frazier added a two-run drive in the sixth off Marco Estrada, who gave up six hits and four walks in six innings.
Pena had homered during a 9-4 loss to the Cubs on Wednesday night. He hit for Bailey with the score tied at 3 in the eighth and connected on the first pitch from Jim Henderson (2-1) for a two-run homer. Cincinnati sent 11 batters to the plate while scoring five times during the inning.