The Royals had a chance to gain on Baltimore in the race for the American League's second Wild Card spot but instead remained four games back.
The A's battered Royals pitching for 17 hits. Royals starter Dillon Gee never made it out of the fourth, giving up five hits and five runs while walking four.
Khris Davis got the A's going with a three-run blast off Gee into the fountains beyond left-center field, his 36th. That A's added three more in the fourth, two coming home on Stephen Vogt's two-run single.