The Manchester United manager saw the positives in his side's derby defeat at Old Trafford and believes James Milner's opening goal should have been waved off for interference.
The Netherlands international helped provide the assist for United's equalizer with an in-swinging free kick, although he was once again profligate in front of goal as he again failed to find the back of the net.
But Ferguson was quick to praise the former Arsenal striker's contribution and is sure that the Red Devils are still on course in their pursuit of the Premier League title, despite Sergio Aguero's winning goal cutting the gap to 12 points with seven games to go.
"There were a lot of plus points for us," Ferguson told Sky Sports following the match. "The evidence is clear that our form is good, I've no complaints about that. I thought Van Persie was absolutely fantastic today. I brought Wayne Rooney back – he almost played 90 minutes. That'll bring him on again, because he's missed a couple of games.
"Looking at the whole thing it's not a bad day for us in terms of performance level. You don't want to lose a derby game, but we're OK.
"It was a very intense game, competitive - two of the best teams in the country. The opening period was end to end but nothing quite happened. We were quite dangerous a few times on the counterattack where we should have done better, but I thought second half we were the better team - I thought we were unlucky to lose it."
The United manager rued his side's defending in allowing Aguero to break into the box to score the winning goal and suggests that James Milner's opener should have been ruled out for offside.
"We must look at ourselves in terms of the goals we've lost," Ferguson said. "We know Aguero's a fantastic finisher. That's what they brought him on for, but we gave him a lot of room for that.
"The first goal? Certainly Tevez is interfering with play, but the linesman on that side, no way was he giving it. But it's disappointing because he's clearly in the road of the goalkeeper – if that's not interference then I don't know what is."