First, Seth Smith clubbed his 11th home run of the season off Yankees closer Rafael Soriano in the ninth, evening up the game at 4.
Then in the 12th, designated hitter Coco Crisp singled with two outs to drive in Derek Norris, who had been moved over to second thanks to second baseman Jemile Weeks' bunt hit attempt.
It was the A's 11th walk-off win of the season, adding to their Major League-best total.
"It just felt like if we get a guy to second base and have the right hitter up there, like we did with Coco today, that something good would happen," A's manager Bob Melvin said. "When I saw [Weeks' bunt], now we're at second base, it kind of dawned on me, we got the right guy coming to the plate."
At this point, nothing Oakland does seems improbable, but this stands as another unlikely victory given the way it unfolded. Starting pitcher Bartolo Colon allowed five hits and three runs in the third inning, leading Melvin to say it looked like it was going to end up "12-0."
But the A's came back, partly thanks to solo home runs from third baseman Brandon Inge -- who came into Sunday's game sitting at the Mendoza line of .200 -- and catcher Kurt Suzuki, who was carrying a career-long 78-game homerless streak to the plate, dating back to last September.
And while Smith has plenty of power, his game-tying shot came against a pitcher in Soriano who hadn't allowed a home run all season long. Smith figured Soriano would throw another breaking ball after the closer threw one on a 2-0 count, and he was right, smashing it out to center field.
"I don't have an excuse for that," Soriano said. "It's one pitch. The guy, I don't think he hit it that good. He hit a home run. Right now, all four games, the team is struggling, but we'll come back to Seattle and try to play better."
Add it all up, and the A's went 5-1 on a homestand against the teams with the two best records in baseball in the Rangers and the Yankees.
Many labeled these six games a test of whether an upstart Oakland team was truly capable of contending this season. Melvin and the players refuse to talk about the playoff race because the end of the season is so far away, but they do admit that they're having plenty of fun right now.
"It definitely feels good to battle and be victorious against the best teams, on paper, in the game," Crisp said. "You can look up and down a lot of lineups like Detroit, or the Angels, the teams with high payrolls. Obviously they have high payrolls for a reason, because the players on the team deserve it. When we battle against those guys and come out with wins, it's definitely a great feeling."
Oakland wouldn't have been in position for the win were it not for the efforts of the bullpen. Jordan Norberto, Grant Balfour and Jerry Blevins combined to throw 5 1/3 innings of scoreless relief after Colon exited the game in the seventh inning.
It wasn't necessarily a surprise, since the team's relief corp has had the best ERA in the American League for a while now, but that didn't make it any less impressive.
Blevins, pitching the final two frames, came up particularly big. While he was on the mound in the top of the 12th, right fielder Josh Reddick lost a ball hit by Mark Teixeira in a blinding sun and couldn't secure the catch, giving the Yankees a man on second to lead off the inning.
But Blevins got out of the jam, giving the A's another chance in the bottom of the 12th. It was a "great team victory" in Melvin's mind, and one that added to Oakland's remarkable recent run.
"To go 5-1 was pretty remarkable, and beating these guys four in a row with as well as they were playing coming in here was probably a little bit unexpected," Melvin said. "But like I said, if you really try to individualize each day and have expectations to win each day, you don't get too far ahead of yourselves.
"Boy, again, terrific series."