Mario Balotelli and substitute Edin Dzeko both struck twice with Sergio Aguero (pictured) and the outstanding David Silva completing the embarrassment as City ran riot at the home of their fiercest rivals.
On a wretched afternoon for United, Northern Ireland defender Jonny Evans was red carded early in the second half when his side trailed by a single goal.
He will faces suspension and another fight to regain his place after his latest nightmare.
The outcome could have been even worse for United.
City created a hatful of other chances, but their joyous fans, in the shadow of their Red Devil counterparts for decades, deliriously settled for a tennis score rather than a cricket score.
The astonishing victory took City five points clear of United at the top of the Premier League table and made Roberto Mancini’s men odds on favourites for the title.
There is a long way to go yet, but this result adds to the growing evidence that a shift of power in Manchester and English football is on the way.
Mancini tried to play down his side’s success, but Ferguson cut straight to the chase admitting: “It was our worst ever day. It’s the worst result in my history, ever. Even as a player, I don’t think I ever lost 6-1.”
Ferguson stated that the horrendous defeat set a challenge for himself and his players, bullishly adding that they will be up to it.
“We'll come back,” he said. “By January we'll be okay. We usually get the show on the road in the second half of the season and that will have to be the case.
“We've played all the teams around us and they have all to play each other so the second half of the season is important to us now.
“We will react, no question about that. It's a perfect result for us to react to because there is a lot of embarassment in the dressing room and that will make an impact.”
Cool and collected Mancini said: “It was important to beat such a fantastic team, but in the end it is three points. We don't take six points for this game.”
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