Lester struck out seven over six innings for his second win in his past seven games. Chapman, acquired from the Yankees on Monday, picked up his first save with the Cubs on Thursday, and he was able to sit back and watch, along with the 40,951 fans at Wrigley Field.
Mariners starter Hisashi Iwakuma served up a two-run single to Chris Coghlan in the second and Heyward's homer in the third, which was the outfielder's first since June 11. Iwakuma lasted three innings, his shortest start of the season.
The Cubs, now 11-13 in July, need to sweep the series to finish the month at .