United shockingly fell behind to a Jamie Mackie goal seven minutes, the 14th time this season they've conceded first, into the second half but then hit back with a three goal blitzkrieg in nine minutes to sew up all three points at Old Trafford.
Jonny Evans equalised with his third of the season before Darren Fletcher and Javier Hernandez completed the comeback.
"We played for 10 or 15 minutes," said Ferguson.
"That was the sum total of our real performance from Manchester United.
"Of course it is frustrating we keep ending up in that position but when they scored it definitely sparked us up."
Ferguson hailed the introduction of Anderson for Paul Scholes, who will miss Wednesday's encounter with West Ham through suspension, as pivotal.
However, Fletcher's goal was more notable, his first in the Premier League in 13 months as he made his first start in the competition for a year.
"Everyone is delighted," he said.
"It has been a long road back for him. It is the first time he has played twice in one week. He didn't let us down again. He never does.
"It is lovely to have him back like that. We will look at Wednesday but he has made a great contribution today."
Ferguson also confirmed winger Antonio Valencia would miss the West Ham game with a hip injury.
"Antonio has had a bit of pain there for the last couple of weeks," said Ferguson.
"He has been playing with it but he never mentioned it.
"When we asked him, he said it was sore.
"It won't be too long. He should be ready for next week."
Meanwhile QPR's stand-in boss Mark Bowen launched a passionate defence of Mark Hughes' managerial reign following the defeat.Hughes was sacked on Friday morning and has already been replaced by Harry Redknapp.
The new man was present at Old Trafford and will take training for the first time on Sunday, leaving Bowen facing an uncertain future.
However, the Welshman insists Hughes had improved Rangers, even though they remain at the foot of the Barclays Premier League with only four points, the worst return in the competition's history from the first 13 games.
"People ask me what went wrong but when this club stayed up on the last day of last season, clubs like Southampton and Reading had a better squad than us," said Bowen.
"They had players who had been together and had success together.
"At times we have been criticised for the number of players who have left.
"Not one player we have let go is anywhere near the Premier League now.
"We have brought good players into the club. I have seen it every day in training. Maybe at times a few of the lads have been found wanting."
Bowen denied reports Hughes had walked off the training ground on Friday, having been informed by chief executive Philip Beard he was going to be sacked no matter what the outcome of Saturday's game.
"We were preparing for training and putting our ideas together about what we were going to do when Philip knocked on the door," he said.
"No-one was called over. It was all handled with dignity."
Redknapp left four minutes before the end of the game, with Bowen confirming he had no input.
"I have not spoken to Harry and he has not spoken to the players," he said. "It has been difficult.
"Football is an emotive game and yesterday [Friday] was a desperate day. Mark is my friend.
"I just said I would prepare the team to give everything it has got."