Mike Sweeney hit a go-ahead, two-run double in a four-run eighth inning, and the Royals beat the A's 5-3 Friday night to complete a doubleheader sweep.
The A's had just three hits in the second game and nine in the doubleheader.
"You're not going to win many games with three hits," Oakland manager Ken Macha said.
Coming in, the Athletics had won six straight, 13 of 14 and 17 of 20, but their AL West lead over the second-place Los Angeles Angels was cut from six games to 4½. Oakland had won 12 in a row at Kansas City since May 30, 2003, outscoring the Royals 95-30 in that span.
"They've been playing very well," Macha said. "They hustled their tails off. There are no easy wins in this league. They've got some power arms out there, and we just didn't swing the bats."
The Royals last swept a doubleheader Sept. 20, 2005, when they hosted Detroit. Oakland played its first doubleheader since June 8, 2003, when it was swept at Philadelphia.
"We got the job done against one of the hottest teams in baseball," Sweeney said. "We want the people in Kansas City to start seeing blue. We're glad we came through against Huston in the eighth. He's one of the best closers in baseball."
Huston Street relieved, Mark Teahen singled and Sweeney doubled to left, taking third on the throw home. Emil Brown followed with a sacrifice fly off Street, who blew a save for the eighth time in 37 opportunities. Street (4-4) left the game with a strained right groin, and the A's said he was day to day.
"He just got more sore as time went on," Oakland trainer Larry Davis said. "He felt it earlier, and he kept on pitching."
Joe Nelson pitched the ninth for his second save in as many chances. Kansas City starter Jorge De La Rosa gave up two hits and four walks in five innings.
Oakland starter Esteban Loaiza gave up five hits and an unearned run in 6 2/3 innings, striking out seven and walking none. He allowed his only run when shortstop Marco Scutaro bobbled Reggie Sanders' two-out grounder in the seventh and threw low to first as Teahen scored.
"E-Lo pitched a whale of a ballgame," Macha said. "He had good fastball, located well. He had one jam there and should have been out of that, except for a misplay in the field."
Jay Payton had hit a sacrifice fly in the sixth.
"We got their starter out of there with the bases loaded and nobody out," Macha said. "They brought in their former closer and he threw the ball very well. Actually it was a pretty darned good at-bat by Payton to get the one run in."
- Kansas City played its 200th doubleheader, its second in seven days.
- David DeJesus was hit by a pitch leading off the first inning. It was the 10th time this season he has been hit, which tied him for fourth in the AL.
- Kansas City was 5-for-17 with runners in scoring position after going 7-for-40 in its previous four games.