NEW YORK -- Dave Robertson's grip on the eighth inning may only last into next month, but the right-hander has given his team nothing to worry about in his new role setting up for closer Mariano Rivera.

With Rafael Soriano on the disabled list until after the All-Star break and Joba Chamberlain out for the year, Robertson has flourished, holding opponents to one earned run over his last 17 appearances.

"I feel like coming into those jams makes me really have to focus on throwing strikes," said Robertson, who owns a 1.19 ERA in 33 appearances. "In the past, when I've come in and no one's on base, I've tended to walk a couple and still get out.

"I think that's really helped me be able to bear down and pretend it's like a situation like that, and really just throw strikes and go after hitters."

Robertson started the year behind Soriano and Chamberlain on the pecking order, picking up outs in the sixth and sometimes seventh innings and earning praise for his high strikeout rate (14.24 per nine innings).

But he said that his sense is that, by and large, all of the innings he has been thrust into have felt the same.

"It seems like every time I'm in a game, it's a high-pressure game," Robertson said. "I find a way to get outs. Even if it's the eighth inning and there's no one on base, you still have to get outs without letting them score.

"It's a little different with having runners on base, but you still have to do the same thing. You have to get outs and try to keep the game going and get the ball to Mo."

Colon throws 'pen session; simulated game next

NEW YORK -- Bartolo Colon threw 31 pitches in a bullpen session on Friday in Tampa, Fla., the Yankees right-hander's first time on a mound since suffering a strained left hamstring.

"I heard he threw all his pitches, he threw well," said Yankees manager Joe Girardi, who added that Colon will throw a simulated game on Monday. "We'll see how he's feeling after that. Hopefully that goes well and we can continue to move forward with him."

Colon, 37, was injured in a June 11 start against the Indians at Yankee Stadium. After making the team as a non-roster invitee, Colon started the year in the bullpen but moved to the rotation when Phil Hughes went on the disabled list in April.

At the time of the injury, Colon was 5-3 with a 3.10 ERA. His spot in the rotation has been filled through two starts by right-hander Brian Gordon, who served up three home runs -- two to Chris Heisey -- in his losing outing on Wednesday against the Reds in Cincinnati.

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Girardi has said that he expects Gordon to make another turn in the rotation. Colon is slated to throw about 50 pitches in Monday's simulated game, and Girardi said that Colon would need to be able to get through the equivalent of six innings before the Yankees would activate him.

"We have to make sure he can cover bases," Girardi said. "We have to make sure he can make quick, sudden stops and starts if they do some stuff on him. He is a good fielder and he reacts quickly off the mound, so we have to make sure he can do that. We have to see how he throws and to see if he's favoring it a little bit."

Hughes celebrates birthday with rehab start

NEW YORK -- Working on his 25th birthday, Yankees right-hander Phil Hughes threw 72 pitches in a 3 1/3-inning Minor League rehab start for Double-A Trenton on Friday.

Hughes allowed one run on three hits in the outing at New Britain, walking two and striking out three. His velocity was reported to hover between 91 and 93 mph.

The rehab start was Hughes' second as he makes his way back to New York's rotation, having gone on the disabled list in April due to inflammation in his pitching shoulder. He appeared last Sunday for Class A Staten Island at Brooklyn, allowing one earned run in 4 1/3 innings in a 61-pitch outing.

It is expected that Hughes will need one more Minor League start, somewhere in the neighborhood of 90 pitches, before the Yankees would consider activating him.

"Our plans are to have him continue to progress," Yankees manager Joe Girardi said before Friday's game. "When we feel that he's ready, he'll be back. He's looked very good in the starts that he's made, and we want that to continue."

Bombers bits

• Right-hander Jeff Marquez said he was seen Thursday by team physician Dr. Christopher Ahmad, who said Marquez has a minor muscle strain in his pitching shoulder. Marquez will not throw for nine days and hopes to be back in the minimum 15 days.

• Tino Martinez has been added to the list of featured invitees to Sunday's Old-Timers' Day game, which will begin at 11:30 a.m. ET. Head athletic trainer Gene Monahan will throw the game's first pitch.

• Third baseman Eric Chavez is progressing "at a pretty slow pace," manager Joe Girardi said. On the disabled list since May 8, Chavez has started baseball activities in Tampa, Fla., and ran from home plate to first base for the first time this week.