Salvador Perez and Franchy Cordero each hit two homers and drove in five runs Wednesday night, as the Royals beat the Cardinals 12-3.
Carlos Martinez (0-3) got rocked for 8 runs on 9 hits. He departed with a strained lower back with two runners on and nobody out in the sixth.
Duffy (4-4) allowed Dexter Fowler‘s single in the fifth inning and loaded the bases in the sixth, but reliever Scott Barlow retired pinch-hitter Brad Miller to preserve a 6-1 lead.
Cincinnati has three games left against Minnesota, while the weary Cardinals face Milwaukee. If needed to settle who is in the playoffs or home-field advantage, the Cardinals also could have two makeup games against Detroit on Monday.
The Cardinals and Reds are tied for second place in the NL Central, 3 and a half game behind first place Chicago, fourth place Brewers are 4 and a half out.
LHP Kwang Hyun Kim (2-0, 1.59 ERA) starts a five game series against the Brewers on Thursday night at Busch Stadium. 6:20 with the pregame, and the first pitch at 7:15 on KIRX.
Royals LHP Kris Bubic (1-6, 3.97) goes Thursday night to open a season-ending four-game set against Detroit at Kauffman Stadium.