Friday's session was the first time he'd thrown off a mound since suffering a left groin strain in the third inning of a July 17 start against the Tampa Bay Rays.
"This was big for me to be able to get all the way back and feel comfortable doing that," said Pettitte, who is scheduled to miss four to five weeks with the Grade 1 (least harmful) strain.
The left-hander said he was "cautious" for the first "20 or 30" pitches of the session, hesitating to push off the rubber at full force. But he was more comfortable after getting through that initial hurdle.
Pettitte said he hoped to throw another bullpen session on Sunday, but added that he hadn't discussed his next step with the Yankees coaching staff. He planned to talk to pitching coach Dave Eiland on Friday.
Yankees general manager Brian Cashman said earlier Friday that he expected Pettitte to return to the mound "sometime in mid-to-late August."
Pettitte's main concern going forward is his arm stamina. He began weight training to strengthen his groin recently and said he didn't feel any pain after the workouts. The 38-year-old is eager to test his endurance and the strength of his groin during his next bullpen session.
"Hopefully I bounce back quick from that," Pettitte said.
Pettitte, who is 11-2 in 18 starts with a 2.88 ERA and was named an AL All-Star, will have to make at least one start in the minor leagues before returning to the Bronx.
"It's hard when they tell you five weeks or whatever," he said. "It just seems so long, you know, and now that you're 2½ weeks into it, you're like, 'OK, just don't have a setback.' "
Ian Begley is a regular contributor to ESPNNewYork.com. Information from The Associated Press was used in this report.