The NL Central leaders improved the best record in the majors to 21-9 and opened a 7½-game lead over Cincinnati. The Brewers are 12-3 on the road.
Peralta (4-1) made his fifth quality start of the season, holding the Reds to three hits and a pair of walks while throwing 110 pitches. Francisco Rodriguez retired the three batters he faced for his 14th save in as many chances.
Peralta doubled with two outs in the fifth off Mike Leake (2-3), who left his first pitch over the plate. Leake gave up seven hits and fanned five as he went eight innings for the second time this season.