Jason Marquis allowed four hits in seven innings to win for the first time in almost two months, as the Cubs posted a 5-to-1 triumph.
It was the eighth victory in nine games for Chicago, which still trails the National League Central leading Brewers by six and a half games.
Chicago jumped ahead early after its season-high seven-game winning streak ended with a 13-to-4 defeat the previous day. Aramis Ramirez doubled in two runs in the first inning, and Derrek Lee and Mark DeRosa singled across runs in the third as the Cubs took a 4-to-nothing lead.
Corey Hart had a leadoff homer for Milwaukee in the sixth.