Robin van Persie and Tom Cleverley both scored in the opening 19 minutes, with Wayne Rooney putting the result beyond doubt just before the hour-mark.
A battling Sunderland refused to give in and Frazier Campbell pulled one back for Martin O’Neill’s men in the 72nd minute, but United held firm to secure the three points.
The result – United’s fifth straight win – keeps them six points clear at the top of the Premier League table after Manchester City won at Newcastle earlier in the day.
“You have to win these games [Manchester derby] and then go for the next one,” Ferguson told BBC Sport. “We will try and keep the momentum going and consistency going. Hopefully by the time New Year is over we’ll be top of the league.”
Reflecting on his side’s overall performance, Ferguson added: “For an hour we were fantastic. Some of our football was very good and we could have scored lots of goals. But I don’t know what happened after that because Sunderland could have had two or three towards the end, it could have been embarrassing.
“I don’t know if we were relaxed or Sunderland picked up the baton 20 minutes from time.”
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