DETROIT – The A's rang up a much-needed victory Thursday, but it came with news that their top starting pitcher is gone for the rest of the regular season.

Left-hander Brett Anderson was diagnosed with a strain of an abdominal muscle, A's manager Bob Melvin announced after a 12-4 rout of the Detroit Tigers.

The A's have overcome every challenge thrown their way as they continue their unlikely attempt to make the postseason.

But losing Anderson is a cruel blow considering they've already lost veteran starters Brandon McCarthy (to injury) and Bartolo Colon (to suspension) within the past month. Anderson, who injured himself during Wednesday's start and left in the third inning, was due to pitch two more times over Oakland's final 13 games.

The A's starting staff now consists of four rookies and journeyman Travis Blackley as they continue this 10-game trip with a three-game series starting tonight against the New York Yankees.

"We're battle-tested," Melvin said. "(Anderson) is a guy that's got ace-type stuff. It hurts to lose a guy like that, but we've lost several starting pitchers over the course of the month."

It's personally tough for Anderson, 24, who returned Aug. 20 from a 13-month layoff after reconstructive elbow surgery. He was 4-2 with a 2.57 ERA in six starts and provided a lift with Colon and McCarthy both out.

"I was throwing the ball well and feeling good," Anderson said. "To have a fluke deal – you don't suspect it at all and the next thing you know you're out again – it's kind of disheartening. But from the team aspect, these guys have been picking each other up through the course of the season. I don't expect anything less now."

Things went rosier for the A's on the field, as they avoided a sweep and snapped their three-game losing streak. They trailed 3-2 before rallying for four runs off Tigers starter Anibal Sanchez in the sixth inning to take the lead for good. They broke the game open with six runs in the ninth.

The A's had altered their rotation even before Anderson's injury. Blackley, a long reliever, will take Dan Straily's start Saturday against the Yankees. Straily will pitch Monday at Texas in Anderson's slot.

Melvin said he prefers the left-hander Blackley to face the Yankees based on matchups and the ballpark.

"You do worry about some of the left-handed hitters in Yankee Stadium and the short porch there," Melvin said. "If (Straily) does pitch in Texas, that's a predominantly right-handed hitting lineup."

Despite the youth and injuries in the rotation, A's starters boast a 3.75 ERA that ranks second in the American League behind Tampa Bay. But the final two weeks will provide a stiff challenge, with three games against the A.L. East-leading Yankees followed by four at Texas.

Oakland finishes the regular season with a six-game homestand against Seattle and Texas.

There appear to be no other options for the rotation than to get by with what it has.

Melvin did not rule out Anderson for the postseason, and with the A's having moved back into a tie for the A.L.'s top wild-card spot with Baltimore, Anderson said, "It'd be a good story if I came back for the (wild-card) play-in game, but we'll see."

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