Not only did Rooney's stoppage-time header book a Wembley showdown with Aston Villa next month, it also avoided United having to face a draining extra half an hour against Manchester City - time that would have sapped legs and made recovery far harder for the encounter at the Emirates.

"Apart from winning us the tie, the good thing about Wayne's goal was that it saved us going into extra time," said the Scotland midfielder.

"That would not have been the ideal preparation for a visit to the Emirates because we know how important this weekend is.

"But that is what being a Manchester United player is all about - a massive semi-final during the week then a few days later another one in the league."

United must travel south without Rio Ferdinand after the central defender picked up an additional match suspension, on top of the automatic three-game ban for violent conduct, because the FA disciplinary panel deemed he made a frivolous appeal against a charge brought against him following his attack on Hull's Craig Fagan last Saturday.

It was always going to be a calculated gamble by Sir Alex Ferguson, who was at least able to name Nemanja Vidic on the bench on Wednesday and does have Jonny Evans and Wes Brown available to fill the central defensive roles against Arsene Wenger's men.

Given Chelsea have now scrambled back to the top of the table and still have a game in hand over their main rivals, the need for victory is acute.

Until last season's Champions League semi-final, United had never won at Arsenal's impressive new home but that decisive victory will have given the Red Devils confidence.

And Ferguson has already recorded a significant victory over Wenger by snapping up Chris Smalling from Fulham.

The 20-year-old will join on a four-year contract in the summer, with Ferguson confirming the signing ends a long-time interest in a player who was playing non-league football with Maidstone two years ago.

"Chris is an extremely talented young defender, who we have been monitoring for some months," said Ferguson.

"He is very quick and reads the game well. He will be a great asset to the club, playing alongside some of the best defenders around and we are delighted to have secured his signature."