At the beginning of the second half, Jonny Evans was sent off for a reckless challenge on Mario Balotelli and City were able to score five goals to complete their annihilation.
This loss by Man United is the biggest home loss for the Red Devils since 1930, when Newcastle won 7-4.
Meanwhile, this ties the biggest win ever by City over United. Back in Jan. 1926, City defeated United 5-0 in a match that also took place at Old Trafford.
After that loss to City in '26, both sides met in an FA Cup semifinal two months later. United went on to win that match 3-0.
Now let's make no mistake, football has dramatically changed in the last 85 years, but the concept of coming back and getting better is something that has not changed.
After nine matches, City find themselves five points clear atop the league table, but there are still 29 more matches left to be played. In the next seven months, there will plenty of change throughout the league and United will have opportunities to recover.
On Tuesday, United will play in the fourth round of the Carling Cup against minnow Aldershot Town. United can use a confidence-boosting win right now and this match against a League Two side will absolutely do that.
Another way this loss will help United is the humiliation factor that has set in. This defeat will provide enough motivation for a long time for United.
The club will be reminded of this match for months and people will continue to say that City are a better side.
Obviously that is not going to work well for Sir Alex Ferguson. There should be no question that he will continue to question his troops about how strong they actually are as a team.
This could cause United's squad to mature earlier than they normally do. Traditionally, United reach a new performance level once the new year starts, but this loss could cause the Red Devils to start playing their best now.
If Fergie starts saying the City match is the worst result ever in his career, then you can absolutely see United start to play at higher level sooner rather than later.
However, this season is far from being done. We will see surprising events happen in the Premier League over the next several months and the club that best reacts to those events will be the champion.
The question is whether or not Manchester United will respond the best. My guess is that they will.
This United squad showed us just how good they could be in the first month of the season and I think that they will once again reach that level soon.
United have suffered big defeats to rivals before, but they always seem to respond well. It shouldn't surprise anyone that they will do it again here.
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