CHICAGO — Jon Lester recovered from a rut of bad starts, pitching six shutout innings that led the Cubs over the Mariners 12-1 Friday for their third straight win.
Jason Heyward and David Ross homered as the NL Central leaders improved to 10-5 since a 1-9 slump.
Seattle lost in its first trip to Wrigley Field since 2007.
Lester had lasted just 16 innings over his previous four starts, going 1-1 with a 10.13 ERA. That skid came after he went 9-3 with a 2.03 ERA in his first 16 starts.
"The guys swung the bats really well," Lester said. "I try to always tell them, 12 runs and an air-tight defense makes a pitcher's job a lot easier."
Mike Montgomery, traded last week from Seattle to the Cubs, pitched the final two innings. He gave up a single to Shawn O'Malley in the ninth for the Mariners' run.
Hisashi Iwakuma had won his last five starts, but gave up five runs and eight hits in three innings. Luis Sardinas moved over from first and pitched a scoreless eighth for the Mariners.
The Cubs, who played their 21,000th game, already led 5-0 when they scored six in the sixth.
Heyward hit his first homer since June 11 and had three RBIs. He had been just 5-for-45 in his previous 13 games.
Kris Bryant reached base all five times for the Cubs. He singled twice, doubled and walked twice.