Rooney gives United the edge as faltering Gunners fire blanks

Manchester United 2 Arsenal 0: Djourou out for season to deepen Arsenal woes as they tumble out of third cup in two weeks despite facing side full of defenders.

Manchester United will play a record 27th FA Cup semi-final at Wembley in five weeks' time, a fortnight before the game at the Emirates that could decide whether they beat Arsenal to the Premier League title.

Regardless of results in between times, Sir Alex Ferguson's team will take a useful psychological advantage into that match after condemning their rivals to elimination from a third competition in the past two weeks. Beaten in the Carling Cup by Birmingham and the Champions' League, less unexpectedly, by Barcelona, the London side were more threatening than at the Nou Camp and passed the ball around as prettily as ever, but could not beat a defiant Edwin van der Sar.

The goalkeeper confirmed afterwards that he will go through with plans to leave the club and he seems determined to depart with a medal – or three. In contrast to a demoralised Arsenal, the Treble is still on for United, who remain three points ahead of them in the League having played a game more, and are favourites to beat Marseille in the Champions' League on Tuesday.

United will also be able to claim that although the number of first-choice players absent from the two teams was about equal, they were able to achieve victory with a lopsided XI in which the Brazilian Da Silva twins, nominally full-backs, found themselves asked to play wide in midfield. They took to it like delighted young ducks to water, Fabio scoring the first goal to end Arsenal's early supremacy before Wayne Rooney added a second soon after the interval.

Arsène Wenger must have looked at the respective team sheets when they arrived from the referee's room and felt that a semi-final place was there for the taking. Instead his fortunate win over United on penalties in the 2005 final remains their last trophy. The squad's mental strength that he has so often boasted of will be tested more than ever after this latest setback; and a sharper edge in attack will be equally important in the weeks to come, starting at West Bromwich Albion on Saturday. One of the evening's few consolations was the return of Aaron Ramsey as a substitute for his first appearance in an Arsenal shirt since breaking a leg over a year ago, but even that satisfaction was countered by a dislocated shoulder injury to Johan Djourou that puts him out for the rest of the season and left Arsenal to finish the game with 10 men.

"I can't fault our effort but things don't go our way at the moment," Wenger said. "Every game against us the goalkeeper is man of the match. Subconsciously I think the disappointment of Barcelona has played a part. I believe we can still do it [in the League] but it's important that we respond very quickly."

Ferguson made the most of having won with a patchwork midfield, claiming he could not have started with either of his veterans Ryan Giggs and Paul Scholes and that Darren Fletcher and Michael Carrick were both injured. "It was a tense game as we expected and both teams played their part," he said. "There was nothing much between the teams but considering the changes we had to make we can be well pleased. The first goal opened the game up and in the second half there could have been more goals for both sides but Edwin made some fantastic saves." Arsenal had certainly gone at the home side with a confidence never evident at the Nou Camp. It was equally clear, however, that the boys from Brazil were determined to enjoy their midfield freedom and after combining to make one excellent chance they set up and took the opening goal. Fabio, operating on the left, fed his brother and took a return pass to supply Rooney, who in turn chipped forward for Javier Hernandez to head at goal. Manuel Almunia could only parry the ball, allowing Fabio to steal ahead of Kieran Gibbs for a tap-in.

That, it transpired, was effectively Fabio's last contribution, as he made way at the interval for Antonio Valencia, warmly received six months after breaking his ankle; all the more welcome once he had contributed to the second goal. His pass down the right allowed Rafael to cross, Djourou just beating Hernandez to the ball but only able to knock it into the air, from where Rooney headed his third goal in four games.

It was desperately frustrating for Arsenal, who had begun the half in busy fashion again. With nothing to lose Wenger strengthened his attack by sending on Marouane Chamakh for Denilson, pushing him up alongside Robin van Persie, who almost immediately curled a left-footed effort just beyond the angle of bar and post. Ferguson, determined that United should not be on the back foot for the remaining half an hour, responded by sending on Giggs and then Scholes, who risked a sending off with two typically wild tackles.

Booking: Man Utd: Scholes.

Attendance: 74,693

Referee: Chris Foy

Man of the match: Van der Sar