Benjani Mwaruwari, the Zimbabwe striker, struck a debut goal to seal Manchester City's first win at Old Trafford since 1974.

Manchester United produced one of their worst performances of the season and defeat left them two points behind Arsenal, the Premier League leaders, who can extend their advantage at home to Blackburn Rovers tomorrow.

Prior to the game, the two teams, with United wearing kit devoid of sponsors names and logos, marched out behind a lone piper to the centre circle. Both Sir Alex Ferguson, the United manager, and Sven-Goran Eriksson, his city counterpart, placed a wreath in memory of the 23 people killed at Munich 50 years ago, when an aeroplane carrying United home from a European Cup tie crashed on take-off.

Then came the minute's silence, the subject of much debate in recent weeks amidst fears of City supporters disrupting the tribute. Yet the silence was observed impeccably inside the ground, a moving tribute which led to the United fans applauding the 3,000 visiting City supporters.

However, outside the ground several loud bangs were heard during the silence. Manchester police are investigating, but the behaviour of City fans inside Old Trafford could not be criticised.

During a frantic start, United nearly opening the scoring in the seventh minute when Ryan Giggs forced a tremendous save from Joe Hart with a left-foot volley. Martin Petrov responded for City by sending a 20-yard shot narrowly over the crossbar.

United, without the suspended Wayne Rooney and Patrice Evra, then tested City again when Cristiano Ronaldo released Carlos Tevez in the penalty area, only for Richard Dunne to deny the Argentinian with a perfectly-timed tackle.

The game continued to swing one way then the next, but the breakthrough came in the 25th minute and it was City that stunned Old Trafford by grabbing the lead through Vassell. It was a goal sparked by a blistering counter-attack by Eriksson's team and it resulted in Petrov's cross picking out Stephen Ireland 12 yards from goal. Ireland's shot was blocked by Edwin van der Sar and the Dutch keeper also saved Vassell's effort from the rebound. But the former England striker pounced on the loose ball and he scored from close range to give City the lead and record his 50th Premier League goal.

It was an outcome that certainly wasn't in the United script, but things went from bad to worse for the home side on the stroke of half-time when Benjani, a transfer-window signing from Portsmouth, doubled City's lead.

Once again, Petrov was a key factor in unlocking the door for City. Having failed to clear his corner properly, United sent the ball back to the winger and his cross was glanced into the far corner by Benjani.

With Rooney absent, United looked bereft of ideas going forward and their hopes of fighting their way back into the game always appeared flimsy, especially with Ronaldo producing one of his worst displays this term.

The brilliance of recent weeks was nowhere to be seen and his second-half display was marked by wayward shooting and inept crossing, just when his team needed him to produce the exact opposite. But the breakthrough that United needed to make never looked like happening until Michael Carrick scored deep into stoppage time but it was too late for Ferguson's men to rescue the points.