Kyle Schwarber hit a three-run homer and made a diving catch in left field, and the Cubs beat the Cincinnati Reds 8-2 on Monday night for their fifth straight victory.
Nicholas Castellanos added a two-run double in the eighth inning as Chicago moved a season-high 14 games above .500. The Cubs have outscored opponents 59-18 during their streak.
The Cubs (82-68) pulled within a half-game of Washington for the top spot in the wild-card standings and stayed two games back of NL Central-leading St. Louis, which held off the Nationals for a 4-2 win.
Steve Cishek, Mills (1-0), Rowan Wick, Kyle Ryan and David Phelps combined for 5 2/3 scoreless innings in relief of an ineffective Cole Hamels.
It was Mills' first major league win in his 17th big league appearance.
Sonny Gray (10-7, 2.80 ERA) faces RHP Yu Darvish (6-6, 3.97 ERA) on Tuesday night in a matchup of two of baseball's best pitchers since the All-Star break. Gray is 4-1 with a 1.29 ERA in his last eight starts for Cincinnati. Darvish struck out 14 while pitching six scoreless innings in Chicago's 4-1 victory at San Diego on Thursday.