The Orioles finally ended their seemingly interminable losing streak at Rogers Centre with a 4-3 win on Thursday afternoon, but they might have lost one of their most important players to injury.

Right-hander Jeremy Guthrie, who was pitching superbly Thursday against the Toronto Blue Jays, could not re-enter in the sixth inning because of an upper back strain. He will be examined by Orioles team physician John Wilckens on Friday and is expected to undergo a MRI.

"I'm going to go see the doctor and get it looked at and see what they say," said Guthrie, who had allowed just one hit and one walk in five scoreless innings. "Who knows? … We'll see where we're at tomorrow morning."

Guthrie said he felt some soreness while throwing a warm-up pitch in the fifth inning but pushed through it and struck out his final batter. He then walked over to athletic trainer Richie Bancells and explained the situation. There was never a thought about going out for the sixth.

"It just wasn't going to happen," said Guthrie, who hasn't had this type of injury previously. "There was enough pain that we're not going to go forward with that, and I would not have been able to throw another pitch probably anywhere near the quality that would be needed in the sixth inning to get somebody out."

Guthrie, who takes pride in his durability, has made 30 or more starts each of the past three seasons, and he threw 200 or more innings in 2009 and 2010. So it was alarming to Orioles manager Buck Showalter when Guthrie couldn't go back after throwing just 64 pitches (41 for strikes).

"Obviously, Jeremy is the type of guy that is going to stay out there if he can," Showalter said. "So that's a little concerning."

Guthrie had struck out five and, according to Showalter, hadn't pitched so well since he shut out the Tampa Bay Rays through eight innings on Opening Day.

"I felt tremendous out there," Guthrie said. "[Catcher Craig Tatum] and I were working well together, and I had a good mix. I was locating down in the zone, and I think that's very important against this team."

Heading into Thursday, the Orioles had lost 16 straight at Rogers Centre, franchise records for both the Orioles and Blue Jays. The last time the Orioles had won in Toronto was Aug. 7, 2009, when Jason Berken picked up the victory, which ended a personal losing streak of nine games.

Strangely, Berken (1-2) was the winner again Thursday, this time in relief a day after he was recalled from Triple-A Norfolk. Berken threw two scoreless innings, striking out two.

"I felt really good. I feel comfortable out there," said Berken, who was demoted to Triple-A on May 20. "I feel like mechanically I am back to where I need to be and the adjustments I made in Norfolk have paid off so far and I've just go to stay after it."

The Orioles (31-35) also halted a four-game losing streak on the season. They made it interesting in the ninth, when closer Kevin Gregg gave up a leadoff homer to Adam Lind before getting the final three outs for his 13th save of the season.

Guthrie was in line for the win after the Orioles scored two runs in the top of the sixth against 24-year-old right-hander Zach Stewart, who was making his major league debut.

Stewart, who was part of the deal that sent Scott Rolen to Cincinnati in 2009, allowed just three singles, a bloop double and a walk through five. But J.J. Hardy led off the sixth with his seventh homer of the season to break the scoreless tie. The Orioles added a run in the inning when Vladimir Guerrero doubled to left to score Nick Markakis. It was Guerrero's 2,500th hit as a big leaguer.

"I think it means he has been around for a long time and he's been really good for a long time," Hardy said. "It's fun to watch him hit."

That's all Stewart gave up in his seven-inning outing. Throwing his fastball in the low 90s and mixing in a good sinker, Stewart allowed seven hits, one walk and two earned runs while striking out four.

It was a similar line to his final start at Double-A a week ago, when he faced the Orioles' Eastern League affiliate, the Bowie Baysox. He gave up five hits and one run in six innings while walking two and striking out six batters in that game.

Stewart was 4-3 with a 4.39 ERA in 12 starts at Double-A New Hampshire, but looked like he belonged in the majors against the Orioles' offense. Stewart retired the Orioles first six batters on 19 pitches.

"I can see why they like him, why they traded for him," Showalter said. "He has got late life on his fastball. And he gave them a good chance to win today. He should be proud of himself, and I know the Blue Jays are."

With Guthrie unable to pitch in the sixth, the Blue Jays scored twice against reliever Jim Johnson, who allowed four singles and was also burned by an error from Ryan Adams. With a runner on first and no outs, Yunel Escobar hit a grounder that bounced out of the rookie second baseman's glove.

After a sacrifice bunt by Corey Patterson moved the runners to second and third, Jose Bautista followed with a two-run single to center. The Blue Jays singled twice more, but Johnson got out of the bases-loaded jam when Edwin Encarnacion grounded into a double play.

The score remained tied until the top of the ninth, when pinch runner Nolan Reimold scored from third on a slow hopper to third byDerrek Lee.

Third baseman Jayson Nix attempted to throw out Reimold, who had pinch-run for Guerrero, but Reimold sneaked under the tag by Toronto catcherJ.P. Arencibia.

Adams picked up his first career RBI with a bases-loaded single up the middle. Blue Jays relievers Jon Rauch (2-3) and Luis Perez did not retire any of the five batters they faced in the ninth.

"I'm so proud of Adams getting a big knock for us there," Showalter said. "I thought that was impressive."

It was a needed insurance run to guarantee the Orioles their first victory here in 22 months.

"It's always nice to get that out of the way," Hardy said. "It's something we're not thinking about out there on the field, but it's always nice to get a win when you know that's going on."

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