OAKLAND, Calif. -- Daric Barton wasn't bothered by the booing he heard in the second inning after dropping Miguel Olivo's fly ball in foul territory. When Olivo homered two pitches later, Oakland's first baseman could only shrug his shoulders.
"It's not the first time it's happened in my life and it's not going to be the last," Barton said. "It's part of the game and you have to have a short-term memory and get over it."
Kurt Suzuki singled home Chris Denorfia with the go-ahead run in the seventh inning and the A's knocked around the Royals' bullpen for the second straight day to deny starter Zack Greinke his fourth win of the year.
Six players had at least two hits for Oakland, which set a season high with 16 hits a night after getting 15 hits against Brian Bannister and four relievers.
"We expect that out of ourselves," Barton said. "We're always having people on base, it's just whether or not we've got the guys in at the right time. If you look at the pitchers we've faced so far and the pitchers we've beat, there's nobody we can't beat."
A day after scoring eight runs in the eighth inning of a 13-2 win, Oakland rallied from a 4-0 deficit and scored three times in its final three at-bats.
Joey Devine (2-0) pitched two shutout innings of relief to earn the win while Huston Street recorded the final four outs for his fifth save in six chances.
Jose Guillen also homered for the struggling Royals, who managed only four hits over the final seven innings. Kansas City has lost three straight and four of five after opening the season 8-5, its best start since 2003.
"Obviously we didn't play up to our capabilities today," manager Trey Hillman said. "We're still making mistakes and I haven't done a very good job of teaching things that we need to do a better job of. I'm accountable for that, bottom line."
Greinke gave up two earned runs in five innings, but the right-hander had nothing to show for it in his attempt to join Boston's Daisuke Matsuzaka as the only four-game winners in the American League. Greinke allowed eight hits and struck out six and left with a 4-3 lead after getting out of two big jams early.
He wound up with no decision after Oakland rallied to tie the game off Ramon Ramirez.
"Putting the runs together was good off a good pitcher," Oakland manager Bob Geren said. "Greinke came in with a (0.75) ERA and he looked like it through the first five innings. He was pretty impressive. To come back and win that game was real good."
Joel Peralta (0-1) gave up two runs in one-third of an inning of relief for the Royals.
Barton, whose leadoff double sparked a three-run fifth off Greinke, played a pivotal role in the comeback. He singled and scored the tying run in the sixth, then hit an RBI triple in the seventh after Suzuki knocked in Denorfia.
In the first two games of the four-game series, Oakland has 31 hits and 19 runs. In their five games before meeting the Royals, the A's had 31 hits and seven runs.
Guillen hit 23 home runs last year for Seattle but hadn't connected since signing a $36 million, three-year contract with the Royals in December. The power drought ended in the first inning when Guillen hit a two-out, three-run homer off A's starter Greg Smith.
Guillen also doubled leading off the ninth and later scored to cut Oakland's lead to 6-5 before Street got pinch-hitter Alberto Callaspo to fly out to left to end the game.
Barton helped Kansas City when he dropped Olivo's pop fly in foul territory in the second inning. Two pitches later Olivo hit his second homer of the year just inside the left field foul pole for a 4-0 lead.
The miscue by Barton marked the 12th consecutive game Oakland has committed an error, matching the team's longest streak since 1983.
"It's not going to matter unless the next pitch he hits a stupid home run," Barton said. "What can you do?"
David DeJesus went 2-for-4 in his return to the Royals lineup. DeJesus, who missed 11 games with a sore ankle, injured his toe when he ran into the wall while shagging batting practice before Thursday's game in Anaheim.
Only two runs off Greinke were earned and matched the total he allowed in his first three starts combined. Greinke went into the game having allowed only nine earned runs in his previous 65 innings. ... The Royals plan to recall RHP Luke Hochevar from Triple-A Omaha to start Sunday's series finale. Hochevar is 1-1 with a 2.60 ERA in three starts for Omaha. ... A's RHP Rich Harden threw long toss for the second time in three days but has yet to do any work off a mound. ... Oakland RF Travis Buck (shin splints) was given the day off.