Ferguson bemoans opening goal after Man Utd beaten by Man City
The champions-elect had their lead over City reduced to 12 points with seven matches remaining after James Milner fired home in the 52nd minute before Sergio Aguero produced a brilliant run and finish after Vincent Kompany's own-goal a minute before the hour-mark.
"It was a very tense, competitive game, it was the two best teams in the country," Ferguson told Sky Sports 1. "The opening period was end to end, but nothing quite happened.
"We were quite dangerous a few times on the counter-attack and we maybe could have done better, but in the second half I thought we were the better team and were unlucky to lose it.
"If you look at the goals we lost, I know Aguero is a fantastic finisher but we gave him a lot of room and for the first goal certainly Tevez is interfering with play, but the linesman that side, there's no way he's giving that, but Tevez is clearly in the road of the keeper. If that's not interference, I don't know what is.
"I was pleased with the performance in the second half. I thought we did really well coming back from 1-0 down.
"If you look at the whole thing it's not a bad day for us in terms of the performance level. It was a very intense game. You don't want to lose a derby game but we're okay."