Salvador Perez hit a go-ahead three-run homer in the sixth inning, the Kansas City bullpen bailed out starter Jackson Kowar and the Royals rallied from an early six-run hole to beat Oakland 10-7.
Kyle Isbel hit his first career homer and Hunter Dozier also went deep for the Royals.
Jake Brentz earned the win and Scott Barlow picked up a save for Kansas City.
Yusmeiro Petit took the loss after giving up Perez's 43rd home run of the season.
The A's have lost three straight and seven of 10 to fall farther out of contention in the AL wild-card race.
