"That was as close as it gets, I guess," Niemann said. "But it was the best-case scenario, as it got the shoulder -- and mostly the meaty part -- and hopefully I'll be back out there in five days."
Miguel Tejada, leading off the Orioles' second, hit a ball up the middle that caught the 6-foot-9 right-hander square on the side of the shoulder; the ball ricocheted to Carlos Pena at first for the unusual 1-3 putout.
Niemann appeared to be in some pain, bending at the waist before being tended to on the mound by a contingent of trainers and manager Joe Maddon. After Niemann threw several pitches, Maddon signaled to the bullpen for Andy Sonnanstine to come into the game.
"I could see in his face that he wanted to stay, but I could also sense that it didn't feel too good," Maddon said. "It's one of those things where he gets stiff and sore very quickly, and there was no sense in leaving him out there."
Niemann didn't feel any real soreness or pain while throwing those test pitches, but "10 minutes after I got done and came [into the clubhouse], it was like, 'I made the right decision,' " he said.
Before he exited, Niemann threw 12 pitches, 10 for strikes, and had retired each of the four hitters he faced.
"I felt great," he said. "All the buildup and anticipation to start the season, and it's finally here ... It was very disappointing. I just have to work to get back out there as soon as I can. ... It's unfortunate, but it happens.
"It tightened up a lot," Niemann said. "But it's just muscle, X-rays are fine, there's nothing really wrong, so I just have to take it day by day and see how it feels."
Maddon will know in the next couple of days whether Niemann will make his next start, which would be against the Orioles in Baltimore on Tuesday.
Niemann was making his first start of the season after leading the team in wins in 2009, when he went 13-6 with a 3.94 ERA in his rookie season.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.