The Cubs improved their MLB-best record to 93-52 and their magic number is one to clinch their first National League Central title since 2008. Chicago secured a playoff berth because St. Louis and San Francisco are the only teams that could pass them in the standings, but since those teams open a four-game series on Thursday both teams wouldn't be able to do so.
The Cardinals began the day a half-game behind the New York Mets and a full game behind the Giants for one of the two wild-card spots.
Lester (17-4) allowed four base runners, none of which got past first. Cubs catcher David Ross threw out two Cardinals trying to steal second and Lester faced just two batters over the minimum.
St. Louis starter Carlos Martinez (14-8) gave up four runs and eight hits in six innings.
Both the Giants and Mets lost their games on Wednesday, so the Giants have a one game lead over the Cardinals for the NL Wild Card lead. The Cardinals trail the Mets by a half game for the second and final wild card playoff spot.