The left-hander had to leave his start against the Orioles after five innings and the Yankees' depleted bullpen -- missing Mariano Rivera -- almost coughed up a five-run lead before finally closing out Baltimore 7-5 on Wednesday to finish a three-game sweep.
The 37-year-old Pettitte felt stiffness above his elbow and in the back of his pitching arm. He went to the hospital for an MRI that showed mild inflammation of his elbow. The team said he will be treated conservatively and evaluated on a day-to-day basis.
"Well, the guys that have been asked to step in have done a good job, so I feel pretty good about the quality of our roster," manager Joe Girardi said. "Could it be tested more now? It's possible."
So far, the mounting injuries haven't derailed one of the strongest starts in team history -- the Yankees have won eight of their first nine series. But after an off day Thursday, New York plays 17 straight, beginning with a three-game series in Boston.
The Yankees hope to get catcher Jorge Posada, who has a strained right calf, back in Boston. Rivera, Girardi said, is more likely to be available.
With Rivera resting a stiff left side muscle and Chamberlain off-limits, Baltimore scored four times against five relievers. It wasn't enough after a rough start.
"Ugly," said Ty Wigginton, who homered and made the last out with the potential tying runs on base. "It was definitely one of our sloppiest games of the year. That being said, the way we battled back was good."
Matt Wieters and Nolan Reimold hit solo homers in the ninth off David Robertson, who was lifted for left-hander Boone Logan with one out. Logan walked pinch-hitter Rhyne Hughes before retiring Lou Montanez and walking Julio Lugo.
Aceves got Wigginton, who hit a two-run homer in the eighth, on a fly to right for his first save this season and the second of his career.
Johnson had three hits, including an infield single up the middle in the eighth. Wigginton, the second baseman, made an error on the play that allowed a run to score and put the Yankees up by four.
Pettitte felt stiffness in his upper forearm during his last start and reported feeling some above his elbow Wednesday while he warmed up.
"We took him in, had the trainer rub it out and it felt fine," Girardi said. "We kept asking him after each inning, the first, the second, the third -- finally, and I had to force it out of him -- in the fifth he said he had felt it again."
Reimold worked a bases-loaded walk off Pettitte in the fourth inning for the Orioles' first run. Wigginton's ninth homer made it 6-3 in the eighth.
Pettitte (4-0) gave up six hits and two walks, improving to 7-0 in his last nine starts against Baltimore. He has lost only twice in his last 20 against the Orioles.
Johnson had a perfect day at the plate. He homered, doubled, singled and walked twice. Swisher had a solo shot in the second and Alex Rodriguez singled home a run in the third.
Orioles pitching coach Rick Kranitz was ejected in the second by plate umpire Paul Emmel, apparently for arguing balls and strikes from the dugout.
David Hernandez (0-4) lasted 3 2/3 innings, allowing six runs on six hits and four walks.
"I had a game plan coming in, trying to establish the lower part of the strike zone," Hernandez said. "It's tough when you don't get those pitches and you have to pitch up in the zone. I didn't make that many good pitches anyway, but it did make it tougher."
After the game, the Orioles optioned left-hander Alberto Castillo to Triple-A Norfolk to make roster room for right-hander Koji Uehara, who will come off the disabled list Thursday. ... Wigginton is tied with Yankees second baseman Robinson Cano for second in the AL in homers. ... Jeter played his 2,164th game, tying Lou Gehrig for second in Yankees history behind Mickey Mantle's 2,401. ... The YES Network, FSN Northwest and DirecTV will broadcast major league baseball's first 3D telecasts when the Yankees play at Seattle on July 10 and 11. They will be available to DirecTV HD customers with 3D sets in New York, Connecticut, north and central New Jersey, northeast Pennsylvania, Washington, Oregon, Alaska and parts of Montana and Idaho. ... Baltimore had two errors.