Pettitte will start Tuesday against the Blue Jays at Yankee Stadium, but he is scheduled to throw only about 70 pitches.
"I expect Andy to be Andy and compete like he always does," manager Joe Girardi said. "The only unfortunate thing is he's not built up to 100 pitches. If you get five good innings out of him, 70 pitches, that would be great."
The 40-year-old went 3-3 with a 3.22 ERA in nine starts after coming out of retirement and rejoining the rotation in May. He struggled in his debut, allowing four runs in 6 1/3 innings, when he admitted to feeling the effects of not standing on a big league mound in more than a year.
But he does not expect the nerves or pressure of a pennant race to affect him this time, only his stamina. His fractured left ankle prevented him from conditioning during most of his rehab, but he was able to maintain his arm strength.
"I'm going to go out there, hope I can get in a good rhythm, have my command and I'll throw the ball well," Pettitte said. "If I don't, if I'm walking guys and my command isn't good, I'm going to get hit, I'm going to get knocked around. That's just the way it is.
"Even though I've been out a couple months, I know what to expect, and [the Blue Jays are] going to be ready for it. I'm looking forward to it being a battle, and I feel like I'm ready for that physically and mentally."