Just a week after the derby defeat that left them six points adrift of their Barclays Premier League title rivals, City produced their best performance of the season at St James' Park.
And, ahead of United's trip to Swansea on Sunday, Ferguson believes his players should take note.
"It was a wake-up call for us," said the Red Devils chief. "City and ourselves will be battling it out and they played really well for the first 20 minutes. But we expect a challenge. It is what we are good at."
It is why Ferguson is approaching the festive programme with such a clear focus, believing if his side have retained their present league leaders status after they have been to Wigan on New Year's Day, they will take some stopping.
"I look at December as an opportunity to gather points," said Ferguson. "If we are top of the league on New Year's Day we know fine well, and so does everyone else, that we are going to be in the ball park at the end of the season."
Ferguson clearly does not want any distractions. And that includes speculation about the futures of his three longest-serving players, which he quashed immediately despite the validity of suggestions Paul Scholes, Ryan Giggs and Rio Ferdinand could all be leaving in the summer.
"It is interesting because Scholesy says very little," said Ferguson.
"I would be surprised if Paul had spoken to some pal without speaking to me - and he hasn't - so we can dismiss that. Ryan could play for another year or two and Rio's form this year has been terrific.
"It is the kind of speculation you expect and comes from our policy of only giving older players one-year contracts but I wouldn't pay it too much credence."