'If he says the ball was going to hit him, why didn't he head it?'

In an explanation at odds with that of his player, Sir Alex Ferguson suggested last night the handball which earned Cristiano Ronaldo the third dismissal of his Manchester United career came as he tried to stop a ball from hitting his face.

Ronaldo's departure, his second in a Manchester derby, will mean he misses one match. It was also shrouded in confusion, with Ferguson positing two theories.

"I have seen it again and he was trying to protect himself from the ball hitting his face, he may have got a little shove as well," he said of Ronaldo's handling of a Wayne Rooney corner. "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."

Ronaldo told a touchline reporter he had "heard a beep" and indicated as he left the field that he had heard a whistle. The handball was particularly mystifying as the 23-year-old had found the elevation to deposit Rooney's corner towards goal.

United had a further four players – Rafael da Silva, Darren Fletcher, Patrice Evra and Michael Carrick – booked during a performance in which they sought to break up City's play and that means they stand to face a £50,000 fine.

Ferguson, perhaps minded not to further contravene the Football Association's Respect campaign and about to face a two-match touchline ban himself, did not comment on what was a commendable refereeing display from Howard Webb.

"But I'm not going to get into the refereeing, we'd be here all day," he said. "Sometimes you have to accept things and we have done that today, with 10 men we proved ourselves."

United's Michael Carrick seemed equally bemused by a sending off which follows the straight red card Ronaldo received in the January 2006 fixture at City. "I couldn't really see what's gone on," he said. "Micah [Richards] went down injured but other than that I don't know what happened.

"He said he heard a beep? That's what he said is it? I don't really know."

Mark Hughes said he believed Ronaldo had to go. "I don't think the referee had any choice," he said. "I don't know what reason he will give for doing it but if he says the ball was going to hit him in the face why didn't he head it? It is a soft sending-off but it was a second bookable offence."

Rooney’s predator's strike earned comparison with Andy Cole from Ferguson. "Cole was a tap-in specialist because he always anticipated situations and Wayne anticipated very well," he said.

Hughes was disappointed with his team's efforts, feeling they were too sluggish, largely due to Thursday's Uefa Cup trip to Schalke. In addition, Robinho could only turn out after having an injection in an ankle injury that had prevented him from training all week. He said: "It was a difficult game for Robinho but we wanted him on because he has been our talisman.

"If I can be diplomatic and say United have great experience of being able to control the game and dictate the momentum of the play. Sometimes they do that by stopping people in their tracks and Shaun [Wright-Phillips] was stopped on numerous occasions."