Adam Loewen of Surrey, B.C., used his first major-league home run to give the Blue Jays a 5-5 tie against his former team, setting the stage for Toronto's win on Jose Bautista's sacrifice fly.
Loewen — who was a starting pitcher with the Orioles for three years — started in centre field for the Blue Jays. His seventh-inning solo shot took Dustin McGowan off the hook for the loss in his first major-league start since July 8, 2008.
Bautista's sacrifice fly later in the inning put the Blue Jays into the lead to stay as they won the rubber match of the three-game series.
Joel Carreno (1-0) pitched the top of the seventh to earn his first major-league win and Frank Francisco earned his 14th save.
Loewen's homer over the centre-field fence against Tommy Hunter (3-4) was one of the biggest moments of his baseball career.
"Right up there with the World Baseball Classic (in 2006) when we (Canada) beat the U.S.," Loewen said. "That was my biggest moment until now just because I went from high-A ball and I was pitching against (Derek) Jeter, (Mark) Teixeira, Ken Griffey, guys I grew up idolizing.
"That was probably more exciting but this feels good too."
Loewen was drafted by the Orioles in the first round as a left-handed pitcher. He was 8-8 with a 5.38 earned-run average in 35 games with Baltimore from 2006-2008. But two stress fractures in his elbow forced him into becoming an outfielder, a position that led him to the Blue Jays.
"I know so many of the guys over there, it was special to do it against them," Loewen said. "The fans at the Rogers Centre are pretty loud and I think hitting a home run compared to striking somebody out, it's a lot louder and a lot better feeling."
McGowan allowed four runs on three hits and five walks in three innings.
Manager John Farrell wasn't surprised McGowan did not appear as sharp as he needed to be.
"And we probably won't see that to its fullest until next year," Farrell said. "This is a rehab year, there's going to be peaks and valleys with arm strength along the way.
"Some inconsistencies with overall command, now we're seeing at this level, those might show up a little bit more."
After coming back from two shoulder surgeries and a long minor-league rehabilitation process, he made his major-league routine with four relief innings against Boston on Tuesday and that outing was encouraging enough to earn him the start.
Loewen has played right and centre field since called up from triple-A Las Vegas last week.
"I think versatility is huge," he said. "Managers always love guys that can move around late in the game. I can play first base if need be, or move to the corner outfield or even centre. I know it helps the team out when you want to pinch hit or move guys around just give them days off.
"I take pride in my defence just as much as anything else."
Cooper, who started at first for Toronto with Adam Lind the designated hitter, led off the bottom of the seventh with his second homer of the season to cut Baltimore's lead to 5-4 before Loewen tied it with a homer to centre.
Mike McCoy followed with a double and Eric Thames singled. Willie Eyre replaced Hunter and Bautista responded by driving in his second run of the game.
"I felt like I was strong," Hunter said. "Reactions from hitters tell you things. I've got to start reading them a little better. Cooper, he hit a pretty good pitch.''
As for the homer by Loewen, Hunter said: "We have the same agent (Michael Moye) so I'm probably going to hear about this for the rest of the time we're together. But you definitely tip your cap. It's one of those things, he's gone through a lot of adversity just in the game of baseball. To come back and be productive in the big leagues not only as a pitcher but as a player, coming back in a different position, is just ridiculous and give him a lot of credit."
McGowan walked two of his first three batters and a wild pitch moved them up a base. Vladimir Guerrero's sacrifice fly put the Orioles ahead 1-0.
The Blue Jays scored two unearned runs in the bottom of the first to take the lead. Orioles' first baseman Mark Reynolds made an error on leadoff hitter McCoy's grounder. Thames singled McCoy to third and Bautista singled to left to score him. A groundout by Brett Lawrie of Langley, B.C., scored Thames.
McGowan walked Reynolds with one out in the second. Nolan Reimold, Robert Andino and Angle strung together singles to produce the tying run.
The Blue Jays moved ahead 3-2 in the third after McCoy broke an 0-for-15 drought with a single, took second on a groundout, moved to third on a fly ball and scored on Lind's single.
The Orioles regained the lead in the fourth. McGowan walked his only two batters in the fourth and Carlos Villanueva took over. With first base open and two out after a ground-out advanced the runners, J.J. Hardy was given an intentional walk after the count reached 3-0 to load the bases. Nick Markakis hit a 3-2 pitch for a two-run single.
The Orioles added a run in the sixth against Shawn Camp who walked Angle to start the inning. Markakis hit a ground-rule double to centre. Guerrero was walked intentionally. The Blue Jays couldn't complete the double play on Matt Wieters' grounder to first and a run scored.
Notes: Attendance at Rogers Centre was 17,235 ... Shortstop Yunel Escobar was not in the lineup Sunday with a swollen left elbow after he was forced from Saturday's game in the second inning after being hit by a pitch. ... Designated hitter Edwin Encarnacion missed his second game in a row after straining his left shoulder on a swing in Friday's game . ...The Blue Jays have Monday off before playing games in Boston on Tuesday and Wednesday.