Alex Ferguson admitted his Manchester United side had been out-fought in their 1-0 defeat at Norwich City.
The result, coupled with a 5-0 victory for Manchester City at home to Aston Villa, meant United ended the day in second place in the Premier League table.
A goal from Anthony Pilkington - a former United youth player - on the hour mark sealed a remarkable win for hard-working Norwich.
"It's disappointing," Ferguson said afterwards. "You have to give credit to Norwich. They battled all over the pitch and defended fantastically well. Their goalkeeper had a really good night also.
"It was a marvellous cross and a magnificent header - there was nothing the goalkeeper could do about that. They deserved the win just because they worked so hard for it.
"We had a lot of possession and one or two half chances without having any great chances. It just wasn't our night."
United had fallen behind on a number of previous occasions this season but had always come back to secure at least a point, and more often than not a victory. Not on this occasion, however.
"We always feel we can do that and the history of the club is like that," Ferguson added.
"The players we have got are used to making comebacks and in matches we are always a threat. We were in some respects tonight also.
"But they defended really well and the goalkeeper made two or three really good saves."
Ferguson had been unable to call upon England forward Wayne Rooney because of tonsillitis. Javier Hernandez, the Mexico forward, made a rare start after netting five goals in the previous eight games mainly from the bench, but he and Robin van Persie did not fashion any clear chances to beat John Ruddy in the home goal.
"You always miss your good players, there's no question about that, but we had plenty of good players on the pitch tonight," Ferguson said.
Norwich had won none of their first seven Premier League games under Chris Hughton, who succeeded Paul Lambert as manager in the summer but are now unbeaten in their last six games in all competitions.
That run began with a home victory over Arsenal by exactly the same score-line but Hughton insisted beating Manchester United was the bigger achievement.
"It's our best result of the season simply because it's Manchester United," he said.
"They tested us more than anybody we have played this season but we were resilient enough. We are on a good run at the moment and we were able to use the confidence we had from that today.
"It's certainly a wonderful achievement to get a result against the likes of these. It's still three points but there is a great feeling tonight because it's Manchester United. After the first few games of the season, where we had a few good performances but didn't get the rub of the green, it is just so vital to pick up points.
"We have proved that we can do that but we know our levels. If we fall below then we can get beat. We need to play at that level, which will give us a chance.
"Over the 90 minutes we deserved what we got. It was such a resilient performance and we limited them to minimal chances. They got a lot of ball into the box because that's what Manchester United do and however well you play it's difficult to stop that. But we defended well as a unit and we could have, with a little more composure at the end, have sealed it a little bit earlier."