Happ made his first start since May 7, when he suffered a skull fracture and a sprained right knee after being struck behind the left ear by a line drive from Tampa Bay's Desmond Jennings. Happ left the field on a stretcher, spent the night in the hospital and had three months of rehabilitation, primarily for the knee.
"It's been a long road to get back but at the same time I felt ready to help us win," Happ said, "and frustrated that it didn't work out today."
Happ, who took a no-decision, went four-plus innings, allowing seven hits and seven runs. He walked three and struck out two.
Brandon Maurer (3-7), who allowed eight baserunners and no runs in 3 1/3 innings, earned the win.
Five Mariners relievers worked the final seven innings, allowing no runs and six hits. It's the first time since Sept. 28, 2011 against Oakland that the bullpen has thrown at least seven scoreless innings.
Danny Farquhar worked an inning for his third save in five chances.
Aaron Harang went just two-plus innings, allowing seven runs and five hits. He walked three and all scored.
It was the shortest outing for Harang this season. The last time he worked just two innings was Oct. 3, 2010, with Cincinnati against Milwaukee. He has had two career one-inning outings.
It's the fourth time he has allowed seven runs, including his previous start, a 10-5 loss to Baltimore.
Presented with a 7-2 lead by the third inning, Happ couldn't deny the fifth-inning rally.
Happ's day ended when he walked Michael Morse.
Aaron Loup (4-4) took over and allowed one run on Michael Saunders' forceout, two on Justin Smoak's double and two on Quintero's home run over the left-field wall, his second. He also had an RBI in the fourth.
It was the largest comeback for a victory since April 11, 2011, also against Toronto when the Mariners were down 7-0 and won 8-7.
"Things have to go your way," Farquhar said. "Our big inning started with a ground ball to Brett Lawrie. It takes a funky bounce, the ball goes into left field, and boom, six runs. Baseball's a funny game. You just can't take anything for granted."
Farquhar was originally drafted by Toronto in 2008, was traded away, traded back and eventually designated for assignment.
"I ended up here. It's nice to face my old team. I've been itching for three days to get in that game," said Farquhar, who has assumed the closer role the past two weeks. "I got in there, got the job done and I'm pretty pumped."
The Mariners touched Happ for two runs in the first. Leadoff batter Brad Miller dribbled a single up the third-base line. Franklin followed with a RBI triple into the right-center gap. That broke his 0-for-27 hitless drought.
Franklin came home on Kyle Seager's right-side groundout.
"They scored two runs early. We built a nice little lead," said Jays manager John Gibbons, whose team took the first two games. "You expect to win those games. We didn't pitch too well today.
"It was good to see (Happ) back there. He looked fine as far as velocity, everything looked good...just not enough strikes. He was too erratic."
The Blue Jays scored five runs in the second. Encarnacion and Lind worked walks, and Lawrie singled through the right side, scoring Encarnacion and sending Lind to third.
Lawrie, born in nearby Langley, British Columbia, was 6 for 11 in the series and reached base eight times with a pair of RBIs.
Harang walked Mark DeRosa to load the bases. Josh Thole, rushed into the starting role minutes before game time because catcher J.P. Arencibia was scratched with right knee soreness, had a two-run double into the left-field seats.
Thole reached third on a right-side groundout and Emilio Bonifacio sent him home with a left-side bunt single.
"It was early in the game," Smoak said. "We told each other, keep putting at-bats together, put some runners on base and get the big hits when we need them."
There were 15 walks issued by both teams, including a season-high nine by the Mariners staff.
Mariners manager Eric Wedge paid a visit to the clubhouse before the game. He has missed the past 16 games after suffering a stroke July 22. He said he is still undergoing tests to get to full recovery and be able to handle the rigors of the job. He's anxious to get back but there is no timetable for his return. . both teams have an off day Thursday. Mariners acting manager Robby Thompson plans to skip Erasmo Ramirez's start Friday to maintain a five-day routine for his other starters. Blue Jays John Gibbons plans to keep all five of his starters on the same rotation. "These guys could all use the (extra) day," he said. . Tests on Jays' RHP Steve Delabar, placed on the 15-day DL Sunday, reveal inflammation in his right shoulder. Nothing serious, Gibbons said. . home umpire Dale Scott was hit hard on his face mast by a Jose Bautista foul ball in the second. He remained in the game for one inning before leaving. Todd Tichenor rotated from first in the third inning to replace him behind the plate.