New York — For the New York Yankees, MRI has become a statistic that's just as important as ERA and RBIs.

Andy Pettitte trudged off in the fifth inning with a back injury.

Chris Stewart limped off after seven with an injured leg.

A 3-2 loss to the Seattle Mariners on Thursday night seemed more significant than just another defeat.

Twelve Yankees already have been on the disabled list this year, costing a total of 332 games. While they lead the AL East at 25-16, how many more injuries can they withstand?

"I think everybody else out of this room probably already felt we passed that point," said Brett Gardner, stranded on third base when Robinson Cano hit a game-ending groundout.

Seeking his 250th win, Pettitte started feeling uncomfortable in the fourth inning, when Seattle took a 2-1 lead on an infield single by Brendan Ryan, who had been in a 5-for-60 slide.

"When I came off in the fourth, it just completely locked up and I got the trainer to give me a little massage down here with some heat, and it loosened up and loosened up really good," Pettitte said.

It lasted only until his first pitch of the fifth, to Jason Bay.

"It completely locked back up on me," Pettitte said. "I couldn't get extended at all. I really just felt like I was kind of cutting everything off and really just trying to throw it in there, just almost slower than slow to tell you the truth."

Pettitte struck out Bay and Kyle Seager. By then, Yankees manager Joe Girardi and pitching coach Larry Rothschild noticed Pettitte's velocity had dropped, and they went to the mound and took him out.

"He is 40 years old, and we're probably going to go through this probably a little bit." Girardi said.

Pettitte missed a start in April because of lower back spasms. This was diagnosed as a tight left trapezius muscle, near his pitching shoulder. It was too soon to determine whether he would miss his next turn.

"There's no doubt I'm getting old. But I don't want to sit there and tell you that that's the exact reason why," Pettitte said. "I look around the league and I see all kind of people on the DL with all kind of problems that are a lot younger than me, too."

Stewart pulled up at third base in the seventh on Cano's infield single, which drew the Yankees within a run. He stayed in for Vernon Wells' inning-ending popout, then was sent for an MRI of his left groin.

"He felt something," Girardi said. "He said it didn't pop."

Stewart, who took over as the Yankees' starting catcher when Francisco Cervelli broke a hand last month, was replaced by Austin Romine. New York doesn't have any other available catchers on its 40-man roster and would have to clear a spot for Bobby Wilson, who has been starting at Triple-A.

"Injuries are a part of the game, and some years you're going to have more than others," Girardi said. "And right now we have a few."

Pettitte (4-3) allowed two runs, four hits and three walks in 4 2-3 innings with five strikeouts, struggling again with his command. In the fourth, he ran into foul territory on the third base side to make a basket catch on Raul Ibanez's low popup but said that didn't figure into his back problem.

Seattle had injury issues, too.

Aaron Harang, Seattle's scheduled starter, felt a twinge in his back Wednesday and notified the Mariners, who in turn told Hector Noesi to prepare for his first big league start of the season.

A 26-year-old right-hander, Noesi was acquired by the Mariners from the Yankees in January 2012 in the trade that sent promising pitcher Michael Pineda to New York and made four relief appearances for Seattle this year. He gave up an unearned run and three hits in 4 1-3 innings, leaving with two on.

Lefty Oliver Perez (1-0), his career revived in Seattle, entered with runners at the corners and struck out Gardner and retired Jayson Nix on a popup.

Seattle also got runs on Dustin Ackley's RBI double in the second and Michael Morse's sixth-inning homer off former Mariners pitcher Shawn Kelley, a drive that bounced off the divider between Monument Park and theYankees bullpen in right-center for his 10th homer this season.

Granderson singled in the second and scored when David Adams doubled for his first big league RBI. In his third game back from a broken arm, Granderson made his third career start at DH and had three hits. He doubled in the eighth but Carter Capps retired rookie David Adams on a popup and struck out Ichiro Suzuki, who one inning earlier singled to stop an 0-for-22 slide.

Tom Wilhelmsen finished to remain perfect in 11 save chances. He allowed a one-out single to Gardner, who stole second and third. He struck out Nix — leaving right-handed batters 0 for 30 against him this year — then retired Cano on a groundout to shortstop.

"What can you say? Nobody's going to feel sorry us," Gardner related. "We can't take the day off tomorrow."

• Girardi said SS Derek Jeter (broken ankle) should be out of a walking boot soon. ... RHP Joba Chamberlain (strained oblique) will need at least one more minor league rehab outing before the Yankees activate him from the DL. ... New York 1B Mark Teixeira (wrist) hit several long homers on curveballs off a pitching machine at the Yankees' minor league complex in Tampa, Fla. 3B Alex Rodriguez, coming back from hip surgery in January, is hitting off a tee and swinging at soft toss flips in a batting cage as he wraps up his second week of baseball activities. ... Travis Hafner (sore right shoulder) took batting practice and hopes to be able to play tonight. ... The Yankees optioned RHP Brett Marshall back to Scranton/Wilkes-Barre and recalled RHP Dellin Betances from the Triple-A team. ... Granderson, in his third game back from a broken arm, made his third career start at DH and had three hits. ... Suziki's seventh-inning single stopped an 0-for-22 skid. ... Seattle OF Franklin Gutierrez (strained right hamstring) was to start a rehab assignment Thursday night at Triple-A Tacoma.