Halladay (13-8) pitched eight strong innings and the Blue Jays beat Oakland 6-1 on Monday night, handing the Athletics their season-high seventh straight loss.
Oakland is a major league-worst 2-14 since the All-Star break, and 9-23 since June 28.
Halladay didn't mind when manager Cito Gaston told him left-hander Scott Downs would handle the ninth, denying Halladay the chance to add to his major league-leading seven complete games.
"You always want to go out, but there always comes a point of being smart," Halladay said. "Being over 100 pitches going through eight innings, [eaving the game] is probably the best thing. You don't get real caught up in the complete games and all that stuff."
Halladay had retired eight in a row and 16 of 18 overall when Bobby Crosby ended his shutout bid with a homer to left in the eighth. It was Crosby's fifth of the year.
That was all Oakland could manage against Halladay, who gave up four hits, walked one and struck out eight.
"It's really something to watch," Gaston said. "It's really my pleasure to be able to manage a guy like Doc. There's not much management to it. You pretty much put him out there and let him go."
The slumping Athletics have scored just 13 runs over their losing streak, and found no relief against Halladay.
"He's one of the best pitchers in the game," Oakland manager Bob Geren said. "There's no doubt. He has a little bit of everything."
Oakland outfielder Jack Cust said a deceptive curveball was Halladay's best pitch.
"I don't know how he gets it to look like that, really," Cust said. "You look up there and it's the same speed, but it seems like it's slower or seems like it's a little sharper. He knows how to pitch."
Halladay agreed that the hook was working better than normal.
"I felt like my curveball was better than it has been my last couple of starts," he said. "For me, that was probably the biggest difference. I had more confidence throwing it in different counts."
Downs worked around a hit and a walk to close it out as Toronto improved to 31-23 at home.
The Athletics came in having won seven straight in Toronto but never looked likely to extend that streak. Oakland right-hander Sean Gallagher allowed the first two runs by hitting batters with the bases loaded, plunking Marco Scutaro in the second and Adam Lind in the third.
"I was trying to nibble way too much, trying to make perfect pitches and ended up missing by a lot most of the time," said Gallagher, who has not won in four starts.
Stairs' single was the only RBI hit for the Blue Jays, who beat Oakland for the third straight game.
Gallagher (1-1) allowed five runs -- four earned -- and four hits in three innings, his shortest start of the year. He walked four and struck out four.
"He had command issues tonight, right from the first batter of the game," Geren said of Gallagher. "His arm angles seemed a bit lower than normal. We'll review it and see if there's any adjustments that need to be made."
Oakland starters are 1-10 with a 6.86 ERA in 16 games since the All-Star break.
The Blue Jays added another run off left-hander Jerry Blevins in the eighth. David Eckstein doubled, moved to third on a single by Alex Rios and scored on Lyle Overbay's fielder's choice, sliding home safely when Kurt Suzuki couldn't handle Jack Hannahan's throw.
Returning to Toronto for the first time since he was released by the Blue Jays on Apr. 19, Oakland DH Frank Thomas was greeted by a mixture of cheers and boos each time he batted. Thomas finished 0-for-2 with a pair of walks.
Gallagher also lost to Toronto on June 13 while pitching for the Chicago Cubs. ... Oakland 3B Eric Chavez will have season-ending surgery next week to repair fraying of the labrum in his right shoulder. ... Toronto 3B Scott Rolen sat out for the second straight day and has missed three of Toronto's past five games because of pain in his surgically repaired right shoulder. ... Toronto INF Joe Inglett (left knee) was a late scratch. Scutaro shifted from second base to third and Eckstein started at second. It was the second time this season Eckstein has played second base. He also played 14 games at second in 2001.