Oakland starter Tyson Ross tried to ignore it on the first pitch, and then tried to fight through it with his second pitch. The third pitch let him know something was wrong.
Ross strained his left oblique and was removed after throwing only seven pitches on Thursday.
"The first pitch to the second hitter felt like a muscle spasm or a cramp," Ross said. "The next pitch I really felt it and the third pitch I said I can't throw with this."
Justin Morneau homered and had three hits and Rene Rivera hit his first home run in nearly five years, and the suddenly resurgent Minnesota Twins beat the Athletics 11-1.
The lanky right-hander gave up a single to Twins' leadoff hitter Denard Span. Ross' 1-1 pitch to Trevor Plouffe got by A's catcher Kurt Suzuki, who was charged with a passed ball.
Ross (3-3) will be evaluated by team trainers before Friday's interleague game in San Francisco.
"Obviously it was a rough start with Tyson being injured with no outs," A's manager Bob Geren said. "You just try to get through 27 outs with your bullpen. It was a rough day, but we'll bounce back. "
Ross wandered around the mound for a few moments before A's trainers were called to the mound. Ross walked off under his own power.
David Purcey rushed in from the bullpen and assumed the count on Plouffe, who grounded out. Span later scored on an RBI single by Jason Kubel.
"We were concerned because we did see him grab his side a little bit," Purcey said. "It's no big deal when the phone rings, but you never expect it that early. I just wanted to go as deep as I could and help save the bullpen."
Nick Blackburn pitched seven solid innings for Minnesota, which has won three straight — all on the road — following a season-high nine-game losing streak.
Plouffe also homered while Michael Cuddyer added three hits for Minnesota. Plouffe homered as part of a six-run eighth inning, the Twins' best of the season.
Hideki Matsui walked and scored for the A's.
Blackburn (3-4) gave up five hits and allowed only one runner past second base to end a three-start winless skid. He struck out two and walked one.
Phil Dumatrait pitched the eighth and Anthony Swarzak worked the ninth to complete the six-hitter.
Blackburn didn't need much support from the offense.
The Twins' right-hander has not surrendered more than two earned runs in his past four starts and has won 10 consecutive decisions in May dating to 2009.
Blackburn only allowed two Oakland runners to reach second base through the first six innings — both with the help of errors. He also got some help from Rivera, who threw out A's leadoff hitter Coco Crisp trying to steal second after Crisp singled in the first.
The A's broke through for a run in the seventh but got little else.
Matsui walked, took third on David DeJesus' single then scored on Mark Ellis' fielder's choice grounder.
The Twins head to Arizona for a three-game interleague series with the Diamondbacks.
Before that, however, Minnesota's players and coaches will attend a funeral for Hall of Famer Harmon Killebrew in Peoria, Ariz. Killebrew will be buried in a private service Monday in his hometown of Payette, Idaho.
Note: Ross is the first A's pitcher to leave after throwing seven pitches or fewer since Omar Olivares did it on June 16, 2000. ... Twins' David Valencia went 2 for 5 to snap an 0-for-19 streak. ... Morneau went 3 for 5 and is 19 for 38 (.500) with six home runs and 15 RBIs in his past 11 games in Oakland. ... A's RHP Brad Ziegler allowed his first run in 17 appearances (13 2-2 innings).