KANSAS CITY, Mo. (AP) Marcus Semien set the tone early, and his Oakland teammates quickly followed.
''The numbers are starting to get off the charts for a leadoff hitter,'' Oakland manager Bob Melvin said. ''The defense he brings, the production he brings, the power he brings, it's fun to watch.''
Jurickson Profar, Matt Chapman and Khris Davis also went deep for the A's, who are locked in a tight race with Cleveland and Tampa Bay for the two American League wild cards. Josh Phegley had a career-high four hits, drove in three runs and scored three times. Three other players had three hits and every starter got at least one as Oakland finished with 22.
''It doesn't matter how we win, just want to win,'' Semien said. ''Today was great to get everybody's bats going, get the confidence up.''
Seth Brown singled in the first two at-bats of his big league career, scored twice and drove in a run.
''Being part of an offensive game like that in your first one, it was something special,'' Brown said. ''It's something I'm never going to forget.''
Homer Bailey (12-8) threw six innings, allowing three runs and eight hits, to improve to 5-2 since coming over to Oakland in a trade with Kansas City.
Oakland scored five runs in both the second and third, backed by Semien's big hits.
Royals starter Brad Keller (7-14) lasted just 1 1/3 innings, exiting after Semien's bases-loaded triple put the A's up 5-0. After retiring his first four hitters, Keller let six straight reach - including three consecutive walks that forced in two runs prior to Semien's triple.
''I felt like I made good pitches to the first four batters, but I gave up kind of a weak groundball and a blooper and it just kind of snowballed from there,'' Keller said.
Brett Phillips curled his first home run of the season, a two-run shot, inside the right field foul pole in the bottom of the inning.
Semien punctuated the five-run third with a two-out, three-run homer, and the A's kept right on scoring. Matt Olson ripped a two-run double in the fifth and Profar added a solo shot in the sixth to make it 15-3. Oakland scored in every inning except the first.
Royals outfielder Alex Gordon made his first career appearance on the mound, throwing 1 1/3 innings and giving up three runs on five hits, including a two-run homer by Chapman.
''Everybody was telling me to throw a changeup but every time I threw a changeup, they crushed it. I should've just stuck to my fastball or my sinker - whatever it was,'' Gordon said. ''The first changeup I threw was to Chapman and obviously he hit that, so I was kind of laughing at him as he was rounding the bases. He smiled back and I was just kind of trying to joke around with him.''
Gordon walked off to a standing ovation from Royals fans after his first pitching appearance since his freshman year at Nebraska.
Kansas City infielder Humberto Arteaga pitched the final 1 2/3 innings and allowed just a solo home run to Davis in the ninth.
Bubba Starling had three hits for the Royals.
CANHA EARNS AL HONOR
Oakland outfielder Mark Canha hit .474 (9 for 19) with four home runs and seven RBIs in five games last week en route to being selected the American League player of the week. Canha has been one of the hottest hitters in baseball in August, batting .370 with five homers and 15 RBIs.
HOME PLATE UMP LEAVES EARLY
Plate umpire Chris Guccione left the game with two outs in the bottom of the sixth. He was hit in the mask by a foul ball earlier. First base ump Mike Everitt took over behind home plate.
The Athletics placed OF Stephen Piscotty on the 10-day injured list with a sprained right ankle and called up Brown from Triple-A Las Vegas. Brown made his major league debut, starting in left field.
The 27-year-old Brown was second in the minor leagues this season with 37 home runs and 104 RBIs.
To make room on the 40-man roster, Oakland designated OF Nick Martini for assignment.
Royals: Manager Ned Yost said LHP Danny Duffy will likely start on Saturday. Duffy has been on the injured list since Aug. 6 with a left hamstring strain. He threw five innings Sunday for Double-A Northwest Arkansas, allowing one run and four hits. ... Yost also said he expects SS Adalberto Mondesi to rejoin the team on Sept. 1, when rosters expand. Mondesi hasn't played since July 16 because of a shoulder injury.
The teams play the second game of their four-game series Tuesday night. Mike Montgomery (3-6) pitches for Kansas City against Mike Fiers (12-3).
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