Mike Montgomery struck out four and walked none and was pulled after Jordy Mercer snapped his 17 1/3-inning scoreless streak with a leadoff homer in the eighth leading the Cubs to a 6-1 victory over the Pittsburgh Pirates on Monday night.
Carl Edwards Jr. got three outs before Wade Davis finished the six-hitter as Chicago moved 2 1/2 games ahead of idle Milwaukee for the top spot in the NL Central.
Trevor Williams (5-7) hung in there with Montgomery, pitching five innings of two-run ball, but Pittsburgh lost for the 11th time in its last 16 games. Mercer went 3 for 3, David Freese had two hits and Andrew McCutchen singled for the Pirates.
Chicago was clinging to a 1-0 lead when Montgomery beat out an infield chopper over Williams' head for a leadoff single in the fifth. He advanced to third on Tommy La Stella's one-out single and scored when Anthony Rizzo's bases-loaded drive pushed McCutchen all the way back to the wall in center for a leaping catch.
The Cubs added three more in the seventh on Alex Avila's bases-loaded infield single and errors on second baseman Sean Rodriguez and catcher Chris Stewart. Rodriguez threw wide of first while trying to retire Avila, and Stewart threw the ball into center field to bring home another run.
Pirates right-hander Chad Kuhl and Cubs right-hander Jake Arrieta pitch in the second game of the series on Tuesday night. Kuhl (6-9, 4.52 ERA) is 3-2 with a 3.33 ERA in five August starts. Arrieta (13-8, 3.49 ERA) has been on a roll since the All-Star break, going 5-1 with a 1.78 ERA in eight outings.