Rickie Weeks and Carlos Gomez added two-run shots, while pitcher Yovani Gallardo and Jeff Bianchi hit solo blasts for the Brewers, who banged out 13 hits in completing a three-game series sweep at Miller Park.
Aramis Ramirez knocked in three runs and Weeks finished 3-for-4 with four runs scored for the Brewers.
Kameron Loe (5-4) earned the victory in relief of Gallardo, who had coughed up seven runs on 11 hits through 4 2/3 innings.
Pirates starter James McDonald (12-7) was roughed up for eight runs (seven earned) on six hits and a walk, lasting just 2 2/3 innings.
Gaby Sanchez and Michael McKenry each homered and drove in three runs, while Garrett Jones went 3-for-3 with a solo shot for the Bucs, who remain 1 1/2 games behind St. Louis for a National League wild card spot.