They completed a sweep of the doubleheader and the series with a 9-6 win in the second game. It was the first doubleheader sweep for the Royals since Aug. 18, 2006, also over the A's in KC.
Gathright replaced Guillen in the outfield for the ninth inning with the opener tied, 4-4.
The Royals' 10th began with A's shortstop Bobby Crosby making an errant throw after fielding Esteban German's grounder. David DeJesus bunted German to second and Mike Aviles was intentionally walked.
So here came Gathright, in Guillen's No. 3 spot. Gee, too bad slugger Guillen wasn't still around to menace A's reliever Joey Devine. Speedster Gathright had a plan.
"I was going to bunt because I looked and the third baseman [Jack Hannahan] was back. I heard them yelling at him so he came in and that just took the bunt away," Gathright said.
Devine fired a 93-mph pitch at Gathright. The left-handed batter slapped it down the third-base line and past Hannahan.
"I know he's throwing the sinker so I just tried to stay inside it and it got through," Gathright said. "I was trying to go to that side of the field -- not necessarily down the line -- but that was my objective, to hit over there to that hole. It got past him and won the game."
German sprinted home from second base and the Royals were jumping and hugging Gathright in the middle of the infield.
Joakim Soria, who pitched two scoreless innings in relief, got his second victory.
The Royals gave starter Brian Bannister a 4-0 lead in a big third inning against left-hander Dana Eveland. Billy Butler smacked a bases-loaded double for two runs, Guillen scored on a wild pitch and Ryan Shealy smacked an RBI single.
In the fifth, with a runner at first and one out, Bannister figured he was doing the right thing by letting Ryan Sweeney's bouncer go past him. He sensed a double play in the offing.
"I purposely let it go. With the speed and direction of it, I figured it'd be right on the base," Bannister said.
The ball was dead on second base and so was shortstop Aviles. Alas, Aviles botched the ball for an error. So the inning wasn't over and the A's got busy and scored three runs, all unearned.
"It's just part of the game," Bannister said. "When you don't strike guys out and there are a lot of balls in play, stuff like that can happen. I just try to stay tough."
But when Daric Barton opened the A's sixth with a home run, they had a 4-4 tie. When Bannister left after seven innings, it was certain that his string of starts without a victory would reach 12.
The game was marked by the return of longtime Royals captain Mike Sweeney who was activated from the disabled list and was the A's designated hitter. For the first time, he played against the Royals in a regular-season game. The small crowd gave him a rousing round of applause in his first at-bat and he flied out.
Sweeney went 0-for-5.
"I buzzed him inside and almost smoked him," Bannister said. "I'm glad I didn't hit him because he's a friend but, out there on the field, it's a little different."
Bannister was relieved by Ramon Ramirez, who set up Soria with a scoreless eighth. And Ramirez was needed again in the second game when the Royals seemed in danger of letting a 9-1 lead slip away.
"It's a situation where you hope you don't have to do something like that," Royals manager Trey Hillman said. "We shouldn't be in that position, we should pitch better but, thankfully, he was OK and he got it done for us."
Ramirez rescued Kip Wells, who issued two walks and gave up an RBI double to Jack Cust in the ninth. Ramirez retired three straight batters, the last two on strikeouts, to record the first save of his career.
After the opener, Ramirez volunteered to pitching coach Bob McClure that he was ready for second-game duty.
"I told him, 'I'm ready, I feel so good I can pitch again,'" Ramirez said.
The victory went to Kyle Davies, who gave up just one run but lasted only five innings because he ran up a whopping 101 pitches.
"You don't want that but I made a lot of good pitches and we won the ballgame," Davies said. "Obviously you don't want to throw 100 pitches in five innings but, on the other hand, you only give up one run and there weren't a lot of balls hit hard."
Guillen drove in three runs in the second game. DeJesus had three hits in each game. Aviles had three hits in the nightcap and is 11-for-24 (.458) in his last six games.
And Butler had a three-double night, extending his hitting streak to 10 games (19-for-40, .475 with 11 RBIs).
The Royals, after a bleak 7-20 August, are a bright 3-0 in September.
"I think it's very big, not only big for the atmosphere we want to finish the season with but it's big for our fan base," Hillman said. "It's gone through a lot of peaks but a lot more valleys this season."