The Cubs rallied without Javy Baez and Anthony Rizz, who left Sunday's game early, thumping the Pittsburgh Pirates 16-6 to finish an impressive three-game sweep.
Rizzo was injured fielding a bunt at first base in the third inning. X-rays showed no fractures, and an MRI has been scheduled for Monday.
The Cubs maintained their one-game lead over Milwaukee for the second NL wild card. The Nationals are 1 1/2 games ahead of Chicago for the first wild card.
Kris Bryant homered twice, and Ian Happ, Kyle Schwarber and Jonathan Lucroy also connected as Chicago battered Pittsburgh for a third straight day. The Cubs scored a total of 47 runs on 49 hits in completing the sweep.
Chicago starter Jose Quintana was pulled after allowing five runs in the third inning, when he fell apart following Rizzo's injury.
After Erik Gonzalez's leadoff double, Pirates starter Trevor Williams bunted toward third base. Rizzo charged aggressively from first and rolled his ankle a few steps before fielding the ball. He threw wide to first base and dropped to the ground in pain.
Brad Wieck (1-1) later replaced Quintana with two on and struck out both batters he faced to end the inning.
Cole Hamels (7-7, 3.89 ERA) starts Monday night in the opener of a three-game series against the Reds. RHP Sonny Gray (10-7, 2.80) pitches for Cincinnati.