The 37-year-old, who has been coaching and training with the club's reserves, came on as a 59th-minute substitute shortly after his return to action for the rest of the season was made public and he was heavily involved as United held off a fightback by 10-man City.
United have suffered a succession of injury problems this season, with central midfielders Tom Cleverley, Darren Fletcher and Anderson ruled out for large chunks of the campaign.
"He has kept himself in great shape and I always felt that he had another season in him," manager Sir Alex Ferguson said in a statement. "It's terrific to have him back."
"I've been pretty clear since I stopped playing that I miss it," he said.
"I'm delighted the manager feels I can still make a contribution to the team and I'm looking forward to playing my part in trying to bring more success to this great club."
"It was a bit of a shock to be honest, we didn't know until we were in the dressing room, but he's a great player," said striker Wayne Rooney.
