Wayne Rooney was so focused on putting Man United ahead in the derby with City that he forgot it was his 100th club goal.

Rooney's tap-in, three minutes before half-time after Joe Hart had parried Michael Carrick's angled drive into his path, allowed United to claim victory despite having Cristiano Ronaldo sent off for a second bookable defence.

It made up for City completing a domestic double over their near neighbours last term and also allowed them to take maximum advantage of Chelsea's shock home defeat to Arsenal.

And it also enabled Rooney to move into three figures in a career that started with Everton, even if the 23-year-old was not instantly aware of what he had done.

"I didn't really think about it being my 100th career goal," he said.

"It was more the fact that it was City away. For it to be the winning goal as well really made it something to be pleased about.

"But of course it is a great achievement. I am delighted to reach 100 and, as I have said before, I am looking to score more often."

Rooney's effort provided some reward for a first half United dominated completely.

City were more of a threat once Mark Hughes introduced Elano at the break but the Red Devils still seemed set to stroll home until Ronaldo saw red.

Already somewhat harshly cautioned, the man expected to collect the Ballon D'Or this week inexplicably parried Rooney's corner with his hands, leaving referee Howard Webb little alternative other than to dismiss him on the same ground Steve Bennett sent him off on three seasons ago.

"He was trying to protect himself from the ball hitting him in the face," said Sir Alex Ferguson.

"He thought he had heard a whistle, he got a little push as well and it is not as if he punched the ball.

"If that had been outside the box it would have been a free-kick and nothing else. But the crowd played a part and he got sent off.

"Sometimes you have to overcome these things and we overcame a lot today."

As Ronaldo is banned for Wednesday's Carling Cup encounter with Blackburn at Old Trafford, when he would not have played anyway, his misdemeanour has not proved costly.

Of more significance will be Patrice Evra's absence from the Premier League encounter with Tottenham at White Hart Lane on December 13 after the French full-back collected his fifth booking of the campaign.