Jemile Weks led off the game with a triple and scored on a Collin Cowgill groundout, but the Royals evened things up in the bottom of the first with an RBI single by Jeff Francoeur.
The A's went ahead in the top of the fourth, as Yoenis Cespedes doubled to lead off the inning and made it to third base on a fielding error, then came home on a wild pitch. Oakland followed that up with a big fifth inning, as they hung a four-spot on the board. Josh Reddick hit a two-run triple, Cespedes hit an RBI single and Kila Ka'aihue hit an RBI double that made it 6-1 Athletics.
The Royals picked up a run each in the bottom of the sixth and seventh innings, but the A's piled on three more runs in the top of the eighth, with an RBI single by Adam Rosales and a run-scoring error that allowed Reddick to reach base.
Cespedes was 3-for-5, while Weeks was 2-for-2 with a pair of walks. Oakland starter Brandon McCarthy improved to 4-3 in his first game back from the DL, going six innings and allowing two runs on eight hits and two walks.
The A's will go for the series win in the rubber game on Sunday.