Arrieta (18-7) allowed five hits and walked one, Anthony Rizzo had three hits and Ben Zobrist drove in two runs as the Cubs tied a team record with their 56th home win. They moved within one victory or one Washington loss of clinching home-field advantage throughout the NL playoffs.
Chicago scored four runs in the first inning off Mike Leake (9-11) and dropped the Cardinals a game behind the Mets and Giants for the two NL wild-card berths.
Pedro Strop came off the disabled list to work the eighth, and Travis Wood and Carl Edwards Jr. finished the five-hitter.
