Manchester derby one of the most exciting ever for Alex Ferguson

Alex Ferguson said Manchester United's 3-2 win at Manchester City was one of the most dramatic of his career after his side moved six points clear in the Premier League on Sunday.

Robin van Persie struck in the second minute of injury time to give United a victory of potentially huge importance, after Wayne Rooney's first-half brace for the visitors had been cancelled out by Yaya Toure and Pablo Zabaleta.

It had looked set to be an afternoon of near misses for United, who saw Ashley Young contentiously denied a goal by the assistant referee's flag less than a minute before Toure reduced the arrears on the hour mark.

However, van Persie's deflected free-kick, which narrowly eluded Joe Hart to nestle in the bottom-left corner, made sure Ferguson's men will go into the Christmas period with an imposing advantage over the defending champions.

"I have not known many more dramatic days than that," Ferguson told Sky Sports. "Today was a special one as City had not lost for two years in the Premier League at home. You could not take your eyes off it.

"I thought we played very well. We had a goal that was perfectly onside ruled out, and they go up the pitch and score.

"That is the kind of game football is and it can kill you and kick you in the teeth. They deserved to come back when it was 2-2, but up to that point, I thought we were far better than them."

There was controversy in the aftermath of van Persie's winner, as United centre-back Rio Ferdinand was left with a bloodied face by an object apparently thrown from the crowd.

A fan also made his way onto the pitch before being ushered away by Hart, while City substitute Carlos Tevez, formerly of United, kicked out at Phil Jones moments before the final whistle.

"It's unfortunate that a City fan runs on and coins are thrown. That shouldn't happen," said Ferguson.

The United manager went on to claim that similar incidents had occurred during his side's 3-2 win at Chelsea in October, which culminated in Chelsea making a claim of racial abuse against referee Mark Clattenburg that was subsequently dismissed by the Football Association.

"The same thing happened at Chelsea, which was masked by all the other things. We could have done without that," Ferguson said.

"At Chelsea, we had half a seat thrown on the pitch, coins, lighters, and nothing done about it. It's a problem.

"As for today (Sunday), I'm going to dismiss it from my mind because it was such a good game."

Rooney's brace took his career tally of goals in the Premier League to 150, but he admitted United had been relieved to hear the final whistle.

"It is great to score here, but I am scoring for United and enjoying it," he told Sky Sports.

"They have had a great home record and to stop it is a great feeling. It was crazy. It has been like that all season for us, and we were hanging on at the end."

City had been well on top until Rooney's 16th-minute opener but coach Roberto Mancini vowed that his side's title defence was not over.

"For 20 minutes they didn't touch the ball and the first chance they got, they scored a goal," he said.

"We recovered very well and we dominated the second half. We wanted to win the game and we had chances.

"We have showed we are a really strong team and we can win this title again. We can't win always. There is a moment when you lose at home and it happened today. But the season is a long one."