Ronaldo equalised from a twice-taken penalty kick in the 54th minute - his 38th goal of a remarkable season - after Emmanuel Adebayor had put Arsenal ahead from close range six minutes earlier.

Then Hargreaves got the winner after 72 minutes with a superb free-kick from 20 yards.

It means United are six points clear of Chelsea, who will be expected to overcome Wigan at Stamford Bridge tonight.

Ferguson said: "The manner in which Ronaldo took the second penalty kick - it was only about six inches inside the post, low down, no goalkeeper in the world could have saved that.

"Jens Lehman guessed right but couldn't get to it - it was a marvellous strike."

It was only Hargreaves's second goal since arriving in a £17million deal from Bayern Munich in the summer and came in front of watching England boss Fabio Capello.

Ferguson added: "I thought Owen would take the free-kick - he is very good at those ones.

"And he has whipped it in brilliantly which you can see from the replays.

"It got inside the post by about half a foot and at that moment I felt that we had a great chance here."

Ferguson remains shocked at the way his team overturned Arsenal's lead at the top and knocked them out of the race with four games to go.

He said: "I would never have expected that and it is a significant result today.

"There were moments in the game when Arsenal probably deserved something from the game but we also produced some great football ourselves."

"We have got four games left, we're three points clear with a great goal difference.

"Obviously if we win the next three games we win the league."

Arsneal boss Arsene Wenger found it a painful experience especially as his side had been knocked out of the Champions League by Liverpool in midweek.

He conceded they were out of the Premier League race and said: "I feel the difference between success and failure is very little.

"We do not feel there is much between ourselves, United and Chelsea when it comes to technical ability and quality.

"So it is difficult to accept we will not win the title.

"I want to win trophies and it is sad we cannot win a trophy this season.

"On the other hand I feel we have done a lot for the Premier League this season by the way we have promoted it.

"We will continue to play the way we do but better. Then the trophies will come.

"Overall I am very proud of my team's performance today. We had to be exceptionally strong after the Liverpool game - and we were."