Royals 8, Mariners 7: All-Star Billy Butler led off the ninth inning with a walk-off home run as host Kansas City won for just the second time in nine games.
Lorenzo Cain belted a two-run shot and Alex Gordon collected three hits and two RBIs for the Royals, who improved to 2-4 on their 10-game homestand.
After Kansas City opened a 7-3 lead, Seattle battled back to forge a tie with one run in the sixth and three in the seventh. The contest remained even until Butler, who finished 3-for-3 with two walks and three runs scored, deposited a 1-1 offering from Josh Kinney (0-1) over the wall in left-center field for his 18th blast of the season.
The homer made a winner of Greg Holland (4-2), who tossed a perfect top of the ninth.
Kyle Seager opened the scoring in the second with a two-out solo homer, but Chris Getz capped a three-run rally for Kansas City in the bottom of the frame with an RBI bunt single. After Casper Wells' two-run blast in the fourth knotted the game at 3-3, Gordon hit a two-run double in the bottom half and Cain launched his second homer in as many nights an inning later for a 7-3 advantage.
Miguel Olivo began Seattle's comeback in the sixth with an RBI single and Jesus Montero cut the deficit to one with a two-run base hit in the seventh. Two batters later, Seager delivered an RBI double, giving him a major league-leading 33 two-out RBIs.
Wells and Ichiro Suzuki had three hits apiece for the Mariners, who have scored 25 runs over the first three games of the four-game series.
GAME NOTEBOOK: Seattle LHP Charlie Furbush was placed on the 15-day disabled list with a strained left triceps, which he suffered in Tuesday's victory. RHP Steve Delabar was recalled from Triple-A Tacoma, one day after being sent down, to fill the roster spot. ... Kansas City LHP Ryan Verdugo was optioned to Triple-A Omaha one day after allowing six runs over 1 2/3 innings in his major-league debut. Fellow LHP Will Smith was recalled and will start Thursday's series finale. ... The Royals were one of six teams that won a draft pick following the first round next year in a competitive balance lottery. Kansas City actually was the big winner of the lottery, capturing the first pick in the drawing.