In Toronto, Dave Collins' two-out single in the seventh inning scored Lloyd Moseby from second with the winning run.
Dave Stieb (15-11) yielded eight hits in seven innings, walked two and struck out two. Randy Moffitt worked the final 1 1/3 innings to earn his 10th save.
"One of the few times I get some runs and I pitch terribly," said Stieb. "Just once, I'd like to put together a good outing with some offense.
"I just had nothing today," he added. "Mentally, I think I was down. I wasn't showing it, but I knew in the back of my mind I didn't have much to work with. I've done it in the past; it just seemed like today it was extremely difficult."
With two out in the seventh, Moseby doubled to left. Collins, who went two for two, then hit the first pitch of Tom Underwood (8-7) to center to score Moseby.
Toronto added an insurance run in the eighth when Tony Fernandez walked, advanced to third on Damaso Garcia's single to center and scored on Rance Mulliniks' sacrifice fly.
The A's had tied the score at 5 in the seventh.With two out, Mike Davis hit his seventh homer, a bases-empty shot, off Stieb.
Toronto took a 2-0 lead in the first on Jesse Barfield's 22nd homer, a two-run shot off Tim Conroy. The A's scored four times for a 4-2 lead in the third. Rickey Henderson tripled in the inning and Dwayne Murphy hit a two-run homer, his 16th of the season.
The Blue Jays pulled even in the fifth on Mulliniks' RBI single and Cliff Johnson's run-scoring ground out. They drew ahead, 5-4, with an unearned run in the sixth on Lopes' throwing error that allowed Collins to score from second.
The victory tied Toronto's team record for victories in a season, 78, set last year when the club finished tied for last place in the AL East.