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05/12/12 7:37 PM ET

Yankees claim former Red Sox lefty Thomas

NEW YORK -- The Yankees announced Saturday that they had claimed left-hander Justin Thomas, a former Red Sox reliever, whom Boston designated for assignment Thursday.

Through seven appearances with the Red Sox, Thomas posted a 7.71 ERA in 4 2/3 innings, walking two and striking out two. Two of those appearances (and one of those runs) came against the Yankees.

Thomas is the second player the Red Sox have lost to an American League East team this season. The Orioles claimed Luis Exposito on April 17.

Thomas also pitched for the Mariners in 2008, and the Pirates in 2010. He has a career ERA of 6.65 in 21 2/3 innings across 27 appearances.

Girardi expecting vintage Pettitte in return start

NEW YORK -- When Andy Pettitte takes the mound on Sunday, he'll be pitching in a Major League game for the first time in 573 days. But Yankees manager Joe Girardi is hoping that the veteran left-hander picks up where he left off.

"I kind of expect him to be what he was in 2010," Girardi said before Saturday's game. "I don't know if that is quite fair after taking a year and a half. That's what I know. That's what I'm using to seeing -- him really grinding out starts, him getting double-play balls. Doing little things to help himself get out of innings."

Pettitte sat out 2011 after posting a 3.28 ERA in 21 starts in 2010. He also made two starts in the postseason, including his last appearance, an Oct. 18 loss to the Rangers in the American League Championship Series. A groin injury limited him to 129 innings in the regular season. Girardi will keep that and Pettitte's age (39 until June 15) in mind.

"I think you have to understand that he's going to want to go out there no matter what, that's his personality," Girardi said. "I think I have to use good judgment. If I think he needs an extra day, I give him an extra day."

Girardi said he expected Pettitte to be able to throw about 100 pitches after making four starts in the Minor Leagues.

"I worry a little about the emotions that could play into tomorrow," Girardi said. "Obviously there's going to be a huge buzz here. When you sit out for a year and a half, you truly realize how much you miss the game."

Pettitte has thrown bullpen sessions at Yankee Stadium, but Girardi has not seen him pitch in person since Spring Training. Catchers Russell Martin and Chris Stewart have not worked with the lefty in a regular-season game.

"It's a different animal when it's the real season and the emotions that go into it," Girardi said. "There will be some challenges, but they'll figure it out. We have experienced catchers and we have an experienced pitcher."

Nix subs at short for Jeter, who serves as DH

NEW YORK -- Jayson Nix made his third start of the year Saturday, but it was his first at shortstop. He spelled Derek Jeter, who served as the Yankees' designated hitter and has appeared in all 33 games this season.

Nix, whose two other starts came in left field, has not played shortstop in a regular-season game since 2010, when he was a member of the Chicago White Sox. His last start at the position came in 2009, but the Yankees played him there in Spring Training this year.

Nix entered Saturday with no hits and no walks in seven plate appearances this season, but he quickly changed that by hitting a two-run home run to cap a four-run second inning that saw the Yankees take a 4-0 lead over the Mariners.

"I have to pick my spots to rest Derek," manager Joe Girardi said. "This is a guy who's played in every game. People were talking about 140, 145 games. We've been fortunate to play him in every game this year, and he's been productive."

Nix became the Yankees' choice after the team demoted Eduardo Nunez following a two-error performance in Thursday's win over the Rays. Nunez will play shortstop and second base in the Minor Leagues as the team looks for other options to rest Jeter and Alex Rodriguez during a stretch of 16 games without an off-day.

"What I worry about is that when they are fatigued, they're going to pull something," Girardi said. "That's my concern. I've been more proactive with Alex than I have been with Derek. I'm just trying to be proactive. We're in a stretch of 16 games. I'm going to have to pick a couple of spots for each of them."

Jeter has started every Yankees game this season, and Rodriguez has started 32 of 33 and appeared in every game. In 2011, he played in only 99 games after missing time due to knee surgery.

Phelps to return to bullpen after rotation stint

NEW YORK -- After two turns in the Yankees' rotation, David Phelps will return to the bullpen ahead of Andy Pettitte's return Sunday.

Phelps lasted a total of 8 2/3 innings in his two starts and allowed two runs on nine hits. He struck out eight and walked four. This season, the 25-year-old righty owns a 3.08 ERA, with 22 strikeouts and 11 walks in 26 1/3 innings. His only decision, a loss, came in his first start against Kansas City.

Manager Joe Girardi said that Phelps, who last pitched Wednesday, would likely be unavailable until Sunday.

The Yankees have 12 pitchers on their active roster ahead of Pettitte's return, but they have carried 13 arms before this season. Right-handed reliever Cody Eppley has already been both optioned to and recalled from Triple-A in 2012. A setback suffered earlier this week by Brett Gardner has allowed outfielder Dewayne Wise an opportunity to spend time with the big league club.

Bombers bits

• Derek Jeter's single in the eighth inning was the 3,141st hit in his career. That ties him with Tony Gwynn for 17th place on the all-time list. Robin Yount sits at 16th, with 3,142.

• The Yankees celebrated Yogi Berra's 87th birthday in a pregame ceremony Saturday. The Hall of Fame catcher rode in from center field on a golf cart driven by former Yankees left-hander Ron Guidry. Jeter and Jennifer Steinbrenner Swindal presented Berra with a cake before Yankee Stadium PA announcer Paul Olden led the crowd in a rendition of "Happy Birthday to You."

• Girardi said before Saturday's game that he would only rarely ask David Robertson to pitch more than one inning. "It's not something we want to do a lot with Robbie," Girardi said. "That has not been who he is. He's been more of a one-inning guy for us in his career." Robertson is 1-for-2 in save situations since Mariano Rivera suffered a season-ending knee injury.

Thomas Boorstein is a reporter for MLB.com. Follow him on Twitter at @MLBoorstein. This story was not subject to the approval of Major League Baseball or its clubs.