The results sees City move five points clear of their rivals at the top of the Premier League table.
“It was our worst ever day,” said Ferguson.
“It’s the worst result in my history, ever. Even as a player I don’t think I ever lost 6-1. That’s challenge for me too.”
Balotelli scored City’s first goal in the first halt. United defender Jonny Evans was sent off in the 47th minute.
“I can’t believe the scoreline. The first goal was a blow for sure but it was retrievable at 1-0,” he added.
“The sending off was a killer for us. We kept attacking when we went 4-1 down and we should have just said: ‘We’ve had our day.’
“I thought with the experience we had with Rio Ferdinand and Patrice Evra we would have realised that. But we just kept attacking. We were so open.
“Sometimes there has to be common sense about it.”
“That’s a perfect result for us to react to,” he added.
“There’s a lot of embarrassment in the dressing room today. They’re all disappointed in there, that will make a difference.”
