The A's have won three straight games and have homered in a season-high seven straight, connecting 11 times in that span.
"Stuff-wise, that was maybe the best he's pitched," Oakland manager Bob Melvin said of Harden. "Really good changeup, changed speeds on his fastball."
Harden (3-2) came in 0-3 with a 5.74 ERA in eight starts against the Blue Jays, including 0-2 with a 13.50 ERA in three starts north of the border. But he was in command for much of this one, allowing five hits over seven innings. He walked two and struck out eight to win his second straight decision.
"I was aware of my past performances here," said Harden, who is from British Columbia on Canada's West Coast. "It felt good to get this one out of the way."
The right-hander has now beaten every AL team except Baltimore, going 0-0 in three career starts against the Orioles.
"It's the most excited I've seen him coming into a dugout after an inning," Melvin said. "He was pumped up after that and he wanted that bad. He wanted to finish that inning and get us in the dugout without them scoring."
Suzuki said Harden's fastball set up the swings and misses on the changeup.
"When he's throwing that fastball down in the zone, you see more swings at the changeup because they know he's throwing (the fastball) in the strike zone," Suzuki said. "He's tough once he does that."
Willingham erased a 1-0 deficit with a two-run drive to left in the sixth, his 18th of the season and fifth in the past 10 games.
Suzuki added some insurance with a leadoff shot in the seventh that landed in the second deck in left, his 10th.
Both homers came off left-hander Brett Cecil, who lost for the first time since July 5 at Boston, snapping a five-start unbeaten streak. Cecil (4-5) allowed three runs and four hits in seven innings. He walked two and struck out five.
"He did well, we just happened to hit a couple of balls out of the yard on him," Willingham said.
Oakland tacked on one more in the ninth. Luis Perez hit David DeJesus with a pitch and was replaced by Shawn Camp. Suzuki reached on a bunt single and Ryan Sweeney followed with a base hit up the middle, scoring DeJesus.
Edwin Encarnacion provided Toronto's only run with a leadoff homer in the second, his 10th.
The crowd of 20,521 gave Lawrie, Toronto's Canadian-born third baseman, a standing ovation before his first home at-bat. Lawrie, who went 5-for-11 in Baltimore over the weekend after being promoted to the majors on Friday, struck out on three pitches.
"It was pretty cool," Lawrie said. "As soon as I stood up there and they gave me a standing ovation, it kind of pumped me up and kind of got my heart going a little bit."
Lawrie finished 0-for-3 with two strikeouts.
Blue Jays outfielder Eric Thames hit a one-out double off Balfour in the eighth, just his second hit in 34 at-bats, and moved to third on Jose Bautista's grounder. Adam Lind lined out to left for the final out.
Athletics DH Hideki Matsui went 0-for-4, ending his hitting streak at 15 games. Matsui had reached base safely in 21 straight games since the All-Star break.
Oakland outfielder Coco Crisp, who strained a calf last Saturday, was expected to miss the entire series at Toronto but felt better after receiving treatment and could return Thursday, Melvin said. ... Conor Jackson returned to Oakland's lineup after missing the past two games because of back spasms. He started at first base. ... The Blue Jays purchased the contract of right-hander Henderson Alvarez from Double-A New Hampshire and outrighted left-hander Wilfredo Ledezma to Triple-A Las Vegas. Alvarez will make his major league debut against Oakland on Wednesday, facing left-hander Gio Gonzalez (9-9).