It was pinch-hitter Kendrys Morales' three-run walk-off homer against righty Grant Balfour in the 10th that did them in this time, less than 24 hours after relievers Jerry Blevins and Ryan Cook were charged for five runs in another loss.
That left the A's staring down a 2-5 road trip, during which their bullpen arms allowed 15 earned runs over 18 2/3 innings. Overall, they've lost seven of their last 10 and nine of 15, and what once was a three-game lead over the Rangers for first place in the West is suddenly a half-game deficit.
Texas is scheduled to play in St. Louis on Sunday night, and a Rangers win would put the A's a full game back; a loss would keep them locked in a tie.
"This trip wasn't a very good one for us," said manager Bob Melvin, flatly. "We didn't expect to go 2-5."
Balfour didn't expect to be out for the 10th -- at least not in a tie game on the road. But Melvin was shorthanded in the bullpen, "and he's our best pitcher," he said.
"I don't know if I had a different mind frame," Balfour said, "because I wasn't expecting the call I guess, waiting for us to score to get in the game, so I didn't have the right mindset going in, maybe."
Oakland's right-hander, riding a 9 1/3-inning scoreless stretch, made quick work of Justin Smoak by way of a groundout. Then he fanned Mike Zunino, but not for an out, as catcher John Jaso scurried for the strike-three wild pitch and threw it wide of first base, leading to Michael Saunders' ensuing base hit to put runners at the corners for Morales.
"I felt like I rushed it a little bit," Jaso said of his throw. "I didn't have to, but I rushed it, and I made a bad throw that kind of cost us a little bit there. ... I would've had him with an accurate throw.
"I just messed up the block. It was my responsibility that I didn't do."
Morales needed just one pitch, a 94-mph fastball, to end the game.
"You strike a guy out, it's tough, because you could've had two outs on six pitches," Balfour said. Got to 3-2, the ball was up to Saunders, I didn't make the pitch, and then the first pitch right there to Morales, and the next thing you know, it's three runs. It kind of happened pretty quick.
"I wanted it away, but when I looked at the video, it was middle. It was more on the down side, but it was middle, and he golfed it out."
Said Morales through his translator: "I was trying to be aggressive. I have the mentality on the bench that I'm always going to be able to come up and hit."
The veteran's walk-off hit spoiled a late comeback by the A's, once down 3-0 because of a pair of Raul Ibanez homers off starter Jarrod Parker. They got two back in the sixth off righty Jeremy Bonderman, and Brandon Moss knotted the game in the eighth via a solo shot to right field.
It was the third career walk-off homer allowed by Balfour, who was stuck with his first loss since June 29, 2012 at Texas.
Now the A's, who finished a stretch of 30 games in 31 days, going 19-11 over that period, get to enjoy an off-day Monday -- the first of three over the next eight days.
"It'll be nice to separate from a tough road trip," Melvin said.