The A's stole four bases, one more than the Angels, and forced a three-base throwing error by Saunders with the threat of another theft by Rajai Davis, who scored the go-ahead run in unconventional style.
Saunders walked Davis leading off the sixth and uncorked a wild throw on a pickoff attempt. Davis scored after the ball rattled around in the Angels' bullpen, right fielder Bobby Abreu finally picked it up and unleashed a strong throw home that was too late.
"I threw the ball away. I haven't done that since I don't remember," Saunders said. "We knew he was going to run -- on first move -- and I just tried to keep him close."
Extending his hitting streak to a career-high 17 games, Morales hammered his 17th homer in the second, tying injured Torii Hunter for the club lead. The opposite-field shot bounced off a TV camera in left. It was upheld by replay.
Morales also singled, walked and lined out to center. That bullet that found the glove of Scott Hairston against reliever Brad Ziegler was one of the key moments in the game, leaving the bases loaded in the fifth.
Replacing a major star averaging $22.5 million for the next eight years -- the Yankees' Mark Teixeira -- Morales is enjoying a breakout season. His 43 extra-base hits are sixth most in the AL, two fewer than Teixeira at a fraction of the cost.
Saunders, slipping to 8-6 with the loss, hasn't won since June 24 and is 3-5 after starting the season with wins in five of his first six decisions.
A 2008 American League All-Star, Saunders struggled with the strike zone all night. He managed to get through the first three innings unscathed while issuing four free passes, finishing with a career-high six walks while allowing five runs, four earned, in six innings.
""I felt I had good command for a couple of hitters, then, boom, I'd lose it," Saunders said. "I threw the ball pretty well. I made maybe one bad pitch, to Crosby. Just one of those up and down nights."
A two-run double by Orlando Cabrera busted it open in the eighth. It was the third hit of the night by the former Angels shortstop.
Trailing, 3-1, the Angels drew even with a pair of fifth-inning runs that chased starter Trevor Cahill. Successive singles by Jeff Mathis, Howard Kendrick and Chone Figgins were followed by two walks, Juan Rivera's tying the game.
Kendrick delivered his RBI single after replacing Erick Aybar, the shortstop having left with dizziness after a slide brought his head into contact with the leg of Cabrera on a double play in the third inning.
The Angels left the bases loaded in the sixth when southpaw Craig Breslow struck out Maicer Izturis. Breslow (2-4) claimed the win when Davis made his mad dash around the bases on Saunders' errant throw.
The A's had turned a one-run deficit into a two-run lead in the fourth with one Bobby Crosby swing. His homer down the left-field line followed Davis' double, steal of third and a walk by Mark Ellis.
"Crosby's homer was the key," Geren said.
Saunders wouldn't argue that point.
"I made maybe one bad pitch, to Crosby," the lefty said. "Just one of those up-and-down nights."
Cabrera singled and scored an insurance run in the seventh on Kurt Suzuki's sacrifice fly against reliever Jason Bulger before doubling home a pair in the eighth.
The Athletics showcased their main strength after Cahill departed, the bullpen shutting out the Angels across 4 1/3 innings. Right-hander Michael Wuertz was especially effective, striking out four of the six men he faced before All-Star Andrew Bailey finished the job. Bailey hasn't yielded a run in his past 14 1/3 innings.