Edwin Encarnacion's second two-run homer of the evening, coming in the bottom of the seventh, was the deciding hit as Toronto got past Boston, 9-7, in the opener of a three-game set from Rogers Centre.
Colby Rasmus and J.P. Arencibia added two hits and an RBI each, while Jose Bautista scored twice and drove in a run for the Blue Jays, who put the brakes on a season-worst four-game losing skid.
"He's been on some kind of roll lately," Blue Jays manager John Gibbons said of Encarnacion. "The guys showed a lot of guts today, a lot of heart. They hung tough."
Steve Delabar (2-1) gave up an unearned run in the seventh inning but was credited with the win.
David Ortiz hit safely twice and drove in four runs for the Red Sox, who fell one victory short of setting a record for the most wins in April. Mike Carp homered and Dustin Pedroia contributed two hits and an RBI in defeat.
Junichi Tazawa (2-1) served up the game-winning blast.
After trailing the entire contest, the Red Sox finally pulled ahead in the seventh. Jacoby Ellsbury got the rally started with a one-out single off Aaron Loup and runners were on the corners after Jays shortstop Munenori Kawasaki's bad throw on a Daniel Nava grounder allowed the latter to reach. Pedroia worked a walk off Delabar to load the bases before Ortiz cleared them with a double for a 7-6 lead.
Momentum changed hands again in the home half, when Bautista walked with two outs and Encarnacion launched his second two-run homer of the contest for an 8-7 Toronto edge.
Rasmus knocked in Arencibia for an insurance run in the following frame, then Casey Janssen retired the side in order in the ninth for his seventh save.
"I thought we did a great job of fighting back into this," Boston manager John Farrell said. "We staked them to a 4-0 lead, we fight back, take the lead with a three-run seventh and gave it right back. They've got a quick strike offense and they swung the bat very well tonight."
Toronto took the lead in the home first, as Rajai Davis walked with one out, stole second and scored on a Bautista double.
The hosts tacked on three more in the home third after Sox catcher Jarrod Saltalamacchia's throwing error on a Bautista dribbler with the bases loaded plated two and Arencibia brought in Bautista with a two-out double.
Boston countered in the fourth as Ortiz led off with a blast to center and Carp followed two batters later with a solo shot of his own, then climbed within 4-3 on Pedroia's fifth-inning RBI hit.
Encarnacion's two-run homer pushed the Jays to a 6-3 edge in the bottom of the inning, but Jonny Gomes' pinch-hit homer off Loup pulled the Sox within two in the sixth.
Encarnacion has two multi-homer efforts this season, with his first coming this past Friday in the Bronx ... Davis scored three runs for the Blue Jays ... Toronto starter Brandon Morrow allowed six hits and three runs, fanning seven and walking three over five innings ... Counterpart Jon Lester lasted six full frames, charged with six hits and six runs -- five earned ... The Red Sox also finished April with 18 victories in both 1998 and 2003 ... Prior to the game, the Red Sox activated pitcher Joel Hanrahan from the 15-day DL, completing the Sunday transaction of sending pitcher Daniel Bard to Double-A Portland.