Sir Alex Ferguson admitted Norwich deserved their 1-0 win at Carrow Road which denied Manchester United the chance to go back to the top of the Barclays Premier League.
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After Manchester City had thrashed Aston Villa 5-0 earlier in the afternoon, only a win would have been enough for United to jump over their neighbours once again.
However, with England striker Wayne Rooney missing because of tonsillitis, the Red Devils produced a lacklustre display as the Canaries - reborn since the international break - produced another composed display to secure a third win in five Premier League games with a fine header from Anthony Pilkington, once on the youth books at United, on the hour.
"Norwich deserved their win because they worked so hard for it, although we had a lot of possession and one or two half chances. We didn't create enough great chances. It just wasn't our night," Ferguson said on ESPN.
"Their goal was a marvellous cross and a great touch for the header. There was nothing our keeper could do about that.
"So you have to give credit to Norwich because they battled well, and their goalkeeper had a good night as well, so it is disappointing."
United had trailed 2-0 at Aston Villa last weekend, but recovered to record a battling victory.
However, the fightback never materialised, even after the introduction of second-half substitutes Paul Scholes and Danny Welbeck.
Ferguson continued: "You always feel that we can do that [come from behind to win] because the history of the club is like that - players have gotten used to making comebacks and we are always a threat in the last few minutes of matches.
"We were tonight in some respects, but they defended really well and the goalkeeper made some saves at vital moments."
Leading scorer Robin van Persie had recovered from the thigh strain which kept him out of Holland's midweek friendly with Germany, while Javier Hernandez also started after his match-winning cameo at Aston Villa last weekend but failed to make an impact.
Ferguson added: "You always miss your good players, but we had plenty of good players on the pitch tonight."
There were four minutes of stoppage time and keeper John Ruddy produced a brilliant saved to turn the ball over after it was deflected off Norwich defender Sebastien Bassong.
At the final whistle, Carrow Road erupted as United went the same way as Arsenal had done four weeks ago.
Norwich are unrecognisably from the side which was taken apart by Liverpool and then Chelsea just last month.
Manager Chris Hughton, appointed in the summer after Paul Lambert left for Villa, felt this performance was the most satisfying of the campaign so far, with a third win in five league games, which have included four clean sheets.
He said: "It is, simply because it is Manchester United.
"They tested us more than anybody we have played against and were resilient enough.
"I suppose with the run we are on, the confidence we have from that we were able to show.
"It is certainly a wonderful achievement."
With Reading and Southampton both also winning today, Hughton knew the importance of getting the victory.
"It is a great feeling tonight because it is Manchester United, but it is still about three points," he said.
"We had a few good performances at the start of the season where we did not get the points from our performances, so it was so vital we can pick up points.
"We have proved we can do, but we have to play our game at that level, because if we fall below that, then we can get beat.
"If we do that, it will give us a chance."