The Brewers got off to a good start when Christian Yelich singled in the first and Ryan Braun homered for a 2-0 lead.
Junior Guerra held that lead until the third when he walked the bases loaded and served up a bases loaded double. The Giants would end up scoring four times in the third and three times in the fifth off of reliever Matt Albers.
Hernan Perez and Travis Shaw also homered for the Brewers, who took three of four in the series.
Guerra fell to 6-7, allowing five runs on five hits with three walks and five strikeouts.
With the Cubs winning in St. Louis on Sunday night, the Brewers trail the Central Division leaders by a game and a half.
The Brewers open a four-game series against the Dodgers in Los Angeles tonight. Freddy Peralta (4-2, 3.74) pitches for the Brewers. Kenta Maeda (7-5, 3.27) goes for the Dodgers. First pitch time is set for 9:10 p.m.