Salvador Perez went 3-for-4 with an RBI and scored twice while Mike Moustakas added a two-run double for the Royals. Duffy (3-5) struck out five and allowed only two baserunners while three relievers combined to finish off the three-hitter.

Shelby Miller (6-5) was tagged with the loss, allowing four runs on seven hits over seven-plus innings. Matt Holliday had two hits for the Cardinals, who have been shut out in consecutive games for the first time since last August.

Miller matched zeroes with Duffy for six innings before he left a fastball up to Gordon, who launched it over the bullpen beyond the right-field fence to open the scoring. Perez and Lorenzo Cain followed with singles and moved up on a wild pitch before Miller hung a breaking ball that Moustakas drove into left-center to plate both runners.

The Royals tacked on three more runs in the eighth, as Perez smacked an RBI single that center fielder Randal Grichuk misplayed, allowing a second run to score, and Cain followed with a sacrifice fly. St. Louis had the leadoff hitter aboard in the seventh and ninth but didn't get either into scoring position.

GAME NOTEBOOK: Holliday has reached base in all 29 home games this season. … Kansas City improved to 21-1 when leading after seven innings and 23-1 when ahead after eight. … Cardinals 3B Matt Carpenter went 0-for-4, snapping his major league-best 14-game hitting streak.