Man United 3-1 Man City:Manchester City's 32-year wait for an Old Trafford win goes on but United moved another step closer in their quest to end a three-year title drought with another derby day triumph.

Cristiano Ronaldo's late goal ensured the Red Devils marched nine points clear of Chelsea at the Premiership summit, although Alex Ferguson might not have been too happy at the way his side failed to cruise home after Wayne Rooney and Louis Saha had put them two in front at the break.

For 12 nervy minutes after Hatem Trabelsi's magnificent effort had breathed fresh life into a contest which saw City battle hard without ever looking likely to win, United were a bundle of nerves.

But Ronaldo calmed them by turning home Rooney's cross six minutes from the end before Bernardo Corradi was sent off at the death.

Having already established a six-point lead over a Chelsea side who face Arsenal at Stamford Bridge tomorrow, there was much more than just local pride at stake for Ferguson's men.

City made their intentions known from the start as Joey Barton clattered into Ronaldo in the opening seconds.

It was the type of treatment Ferguson has long lamented and, given Barton escaped with a warning, it was a little surprising Ben Thatcher was booked for merely blocking off the Portugal winger a little later on.

By that time though, Ronaldo had already played a major role in giving United the flying start they craved.

A major criticism of the youngster is his failure to spot an early pass. No such allegation could be made against him on this occasion though as he seized possession by the right touchline and instantly spotted Rooney unmarked inside the City box.

The cross was accurate but Sylvain Distin should really have cut it out.

Instead, the ball rolled underneath the Frenchman's outstretched leg, straight to Rooney, who gleefully drilled home his eighth goal of the campaign.

He might have had a second not long afterwards too as he strode on to Saha's through ball.

This time, Distin was fully alive to the danger and used all his pace to get back and deny the England man a shooting chance.

It was the kind of last-ditch defending City had to do on more than one occasion, yet, despite the speed of United's attacking play, the visitors enjoyed just as much possession with Joey Barton, turning out despite a recent family bereavement, impressing.

Twice they might have equalised thanks to the prodigious talent of Micah Richards.

Unfortunately for the Blues, on the first occasion, when the 18-year-old won two separate headers inside the United box, Richards was wide of the target. On the second, Richards might have found the net had Georgios Samaras not stopped the ball with his back to goal barely two yards out before turning and scooping his own shot over.

It proved to be a costly miss as United extended their lead before half-time when Blues skipper Richard Dunne was robbed of possession close to his own box.

Instantly, Gabriel Heinze swept the cross into the City box, allowing Saha to bundle home with the aid of a ricochet off Nicky Weaver and the underside of the bar.

Given City's dismal scoring record this term, it should have been game over. It certainly appeared so for most of the second half as United dominated.

The hosts had another keeper as Andreas Isaksson, dogged by injury since his summer arrival from Rennes, was handed his debut as Weaver succumbed to a blow he picked up trying to keep out Saha's goal.

Isaksson got plenty of chance to show City boss Stuart Pearce what he has been missing, three times denying Rooney alone, the latter effort a superb point-blank stop after Ryan Giggs - on his historic 688th appearance - had picked him out with a far post cross.

The value of Isaksson's efforts became apparent when Trabelsi, shown inside by an unsuspecting United defence, let rip with a thunderous 20-yard shot Van der Sar had little chance of keeping out.

All of a sudden, even though Richards was forced out of the battle with a serious-looking injury, there was an obvious state of nervousness among the United team, not helped by the fact that six minutes before City had scored, Ferguson had replaced Saha with John O'Shea, leaving Rooney and Ronaldo as their only attacking outlet.

The Red Devils lived on the edge until redemption arrived when Rooney turned onto Gary Neville's pass, then driving over a cross that flicked off Dunne, straight into the path of Ronaldo, who finished off from close range.