KANSAS CITY, Mo. -- Bruce Chen reaching double figures in victories this season seemed farfetched.
Chen (10-7), who was 1-13 from 2007-09, gave up three runs in the first two innings. He went five innings, allowing three runs, six hits and a walk. Chen, who started the year in the minors, leads the Royals in victories.
"For me to tell you in September I was going to have 10 wins, I would have said no way, I would say you're crazy, but a lot of crazy things have happened," Chen said. "I feel real good with the way I've been pitching. I persevered.
"I started in the minor leagues, then came up here in the bullpen and here I am with 10 wins. It's a long ways from where I left off from last year when I was 1-6, but I still have a chance to keep winning more."
Betemit, who had a home run and four RBI on Tuesday, worked a full count from Trevor Cahill and fouled off the next three pitches before homering just inside the right-field pole in the third inning.
"That was a great at-bat in that situation with the bases loaded and my first grand slam," Betemit said. "He threw me a fastball away. He threw me every pitch and it was around the zone. He threw me a changeup, middle in and I swung the bat good. When I see the ball land in the stairs, I say, 'Yes, I've got it.' I was real happy with that."
Mitch Maier doubled, Jarrod Dyson had an infield single and Billy Butler walked before Betemit's 12th home run that snapped Cahill's 15-inning scoreless streak.
"I had a 2-2 pitch that I thought was pretty close and then he fouled off three pitches," Cahill said. "I thought I might have gotten him to maybe ground one but he didn't. Then I left a pitch up and he hurt me. I made two pretty good pitches [with a full count] but I left one up and in and he turned on it."
Mark Ellis and Kurt Suzuki had run-scoring singles in the A's first. Matt Carson homered in the second on the first pitch from Chen, giving the A's a 3-0 lead.
Joakim Soria worked the ninth for his 38th save in 40 opportunities and he has converted 31 consecutive saves.
The Royals scored 17 runs in beating Cahill and Gio Gonzalez in the final two games of this series.
"We did it against two of the best young pitchers in the American League," Royals manager Ned Yost said. "That was pretty impressive."
Cahill (16-7), who was 7-2 with a 1.69 ERA in his previous nine starts, allowed six runs, six hits and three walks in five innings.
"It just didn't happen tonight," Cahill said. "I didn't have any idea where my fastball was going and my changeup wasn't cutting and running like usual."
While Cahill has limited right-handed hitters to a .184 batting average, the lowest in the majors, he has yielded 11 home runs to right-handed batters. Butler, one of three right-handed hitters in the Kansas City lineup, homered in the fifth with Mike Aviles aboard.
The second-place A's dropped 10 games behind the Texas Rangers, who beat Detroit 11-7, in the AL West. They are a game below .500 (72-73).
Chris Carter went 0 for 4 and is hitless in 24 at-bats to begin his major-league career. The A's record to start a career is 0 for 25 by Bill McNulty in 1972.
Royals 1B coach Rusty Kuntz was named special assistant to the general manager and will report Thursday to the instructional league in Surprise, Ariz., where he will work with outfielders and baserunners. Mike Jirschele, who has managed the Royals Triple-A Omaha affiliate the past eight seasons, will be the 1B coach the remainder of the season. ... Rain delayed the start of the game for 1 hour. ... A's 1B Daric Barton walked in the third, his major-league-leading 101st free pass.