Arrieta (4-4) allowed three hits and one run in seven innings. He walked one and struck out five.
The Cubs had as many home runs as Arrieta allowed hits. Luis Valbuena hit a home run on the first inning while Nate Schierholtz added a two-run shot in the third and Brian Bogusevic had a solo homer in the ninth.
The only Cubs run that did not involve a home run came in the sixth when Arrieta squeezed in Junior Lake with a bunt.
Kyle Lohse (10-10) allowed the first two Chicago home runs. He allowed a total of seven hits and one walk while striking out four in five innings.
Carlos Gomez hit his 21st homer of the year in the seventh to account for the Brewers' run.