SEATTLE -- Andy Pettitte wasn't expecting to feel any discomfort in his left shoulder as he made his way to the bullpen at Safeco Field on Friday. In other words, everything went just as expected.

The 37-year-old left-hander could exhale after firing a normal workload in preparation for his outing on Monday against the Angels, ending a rare respite that the Yankees hope can knock out the fatigue that prompted him to skip a start.

"I wasn't worried at all," Pettitte said. "It's the same old thing. Monday will be good. I'll be happy when I get through Monday and I don't have any problems.

"I want to stand on the mound in the sixth or seventh inning and feel strong like I can keep going when they come pull me, not running on fumes like I was against Baltimore my last start."

Pettitte started to feel some fatigue and achiness in a Sept. 11 start against the Orioles in New York, running out of gas around the fourth inning of a five-inning effort.

It was a brief scare for the Yankees, who have been leaning on Pettitte -- 13-6 with a 4.14 ERA in 29 starts this season -- along with staff ace CC Sabathia as one of their most reliable starters this season.

With A.J. Burnett skidding of late and Joba Chamberlain proving unpredictable, the Yankees must have a healthy and effective Pettitte to feel good about their chances going into their likely entry for the American League Division Series.

"He's real important to us," Yankees manager Joe Girardi said. "There's no doubt about it. That's why we backed him off the start and we're trying to take the cautious route, because we know how important he is to us."

Pettitte said that he will throw again on Saturday and anticipates that he will know by the fourth or fifth inning on Monday if he is in the clear. Girardi is likewise curious to see the results against the Angels, a quality club who just might present an October opponent for New York.

"I'm anxious to see how he does," Girardi said. "I really am. You want to know that one of your horses is in really good shape when he goes out there Monday. You hope that the 10 days rest got him over that hump and he'll go out there and get on a roll like he was on."

Pettitte has been quick to say that this feels nothing like the pain that plagued him down the stretch in 2008, when the Yankees had to take the drastic step of recommending that Pettitte not even throw his regular bullpens between starts.

"I can't even tell you -- I was in such bad shape last year by the time the end of the season got around," Pettitte said. "I just know to make that last start at Yankee Stadium [on Sept. 21], I barely picked up a ball."

Pettitte has not lost since a July 25 start against the Athletics, a span of nine outings in which he has gone 5-0 with a 3.00 ERA, limiting opponents to a .210 batting average. Pettitte still has not decided if he wants to pitch beyond this season, but he is certainly proving that there seems to be plenty in the tank.

"I've been feeling pretty good," Pettitte said. "I hope I can get back in a good rhythm with all my pitches. Before I skipped this last one, I was feeling comfortable with all my pitches and that's really all I care about, getting back in the routine.

"We don't have anything wrapped up, and it's important. I have to go out and pitch well. Let's get this thing wrapped up -- we would love to have home-field advantage, and we're trying to play this thing out and play it out hard. We need to keep going, because we have a tough stretch ahead of us."

In an additional injury update, right-handed reliever Dave Robertson played catch at a distance of 60 feet in the outfield at Safeco Field on Friday and felt good.

Robertson will likely need two more sessions on flat ground to test his stiff right elbow before he can get into a game, which Girardi said that he wanted to do before the end of the season.

The rookie has struck out 54 batters in 36 1/3 innings since being recalled on May 26, a skill set that could make him a valuable bullpen weapon for the Yankees next month.

"We hope that he can probably get in more than two games, but we're not sure," Girardi said.