However Ferguson was less complimentary about William Gallas, who was lucky to escape punishment for kicking Nani.

"I thought Gallas should have been sent off," said Ferguson. "The referee must have a look at that again.

"He kicked Nani from behind and the referee called both over because they sized each other up. He should've been red-carded."

United failed to get going against City on 10 February, in a game that came at the end of a week marking the 50th anniversary of the Munich air disaster.

But they went at Arsenal from the start and United's assistant coach Carlos Queiroz added: "Everyone was attacking and defending together and we played as a unit all of the time.

"It is easy when you play like that because the best players in the team are free to produce the special moments in the game, which we did here.

"Are we surprised by how Arsenal played? No. Arsenal should be surprised by our performance.

"We showed that when we are on top of our game that we are a strong team."

Arsenal manager Arsene Wenger admitted his side were outclassed at Old Trafford.

"It was an off-day for us," Wenger said. "We were beaten everywhere and never looked like coming back.

"When we had a go in the second half we had Emmanuel Eboue sent off and of course it was game over then.

"It was disappointing but this team has given a lot. We were up for it before the game but United were better."

Eboue saw red after a clumsy tackle on Patrice Evra and his was not the only wild challenge of the second half.

Some of the Arsenal players were angry when United midfielder Nani began showboating after his side had gone 4-0 ahead.

But Wenger defended his side, explaining: "We were incensed and most rightly so.

"It is difficult enough to swallow when you are three or four goals down - you do not want to be teased or humiliated."

The Gunners must rebuild for the first leg of their Champions League last-16 tie against AC Milan on Wednesday.

And Wenger is confident that this drubbing will not have an adverse affect on the Gunners.

The Frenchman said: "We still have big enough targets in front of us.

"Now we will try to recover and prepare properly for our next game - we know we need a top-class performance against Milan to have a chance."