Manchester United missed a glorious chance to regain their lead at the top of the table and increase the gap between them and third-placed Chelsea by losing to Norwich, whose goal was scored by former United trainee Anthony Pilkington.
Pilkington scored in the day's late game to extend Norwich's unbeaten run to six games, while the end of United's run of five successive victories in the league means they are now behind rivals Manchester City, who beat Aston Villa comfortably.
For United, this was not only a missed opportunity but a performance that lacked urgency and a cutting edge, particularly worrying with a Champions League date in Galatasaray coming up on Tuesday.
David De Gea, the United goalkeeper, missed the game after having two teeth extracted on Friday, and his team's attack looked equally toothless, at least for the opening 45 minutes.
Without the injured Wayne Rooney United struggled to impose themselves in the final third of the pitch.
Javier Hernandez and Robin van Persie were nullified for the most part by the excellent Michael Turner and Sebastien Bassong, and when Van Persie did get a clear sight of goal before the break but he missed his cue and the ball. The Dutchman's long shot brought a fumbled save from John Ruddy in the opening stages, but the goalkeeper was decisive and determined to keep out a low drive from Ashley Young that went through a thicket of legs towards the far corner of goal.
Pilkington flashed a shot across the United goal after a swift Norwich counter-attack, Wes Hoolahan shot tamely at Anders Lindegaard, and Javier Garrido's low cross flew across goal.
The keeper had another lucky escape early in the second half when he failed to deal with a Snodgrass free-kick, but his blushes were spared as the ball was scrambled clear.
Both sides were playing tidy passing football without looking really dangerous in front of goal, but the deadlock was finally broken on the hour by Pilkington, who spent a year at the United academy in his teens.
Hoolahan and Bradley Johnson exchanged passes patiently in the centre of the pitch, before Hoolahan set Garrido free down the left. The Spaniard crossed towards the near side of the goal area and Pilkington timed his run perfectly to send a powerful header looping over Lindegaard and into the far corner of goal.
The home supporters erupted in delight, conscious of the fact that their team have come a long way since being thrashed 5-2 here by Liverpool at the end of September. After a 4-1 defeat at Chelsea the following week, Chris Hughton set about tightening up his defence, and the result is that Norwich are hard to break down. Those supporters that were beginning to express doubts about Hughton six weeks ago were signing his name, at around the same time Sir Alex Ferguson walked to the touchline to send on Paul Scholes and Danny Welbeck.
The latter went close with two headers in a minute. His first was diverted for a corner, and when that was cleared, he met Michael Carrick's cross with a firm header that Ruddy saved.
Welbeck had another header saved late on, but Norwich should have made it 2-0 in the 89th minute when Jonny Howson was sent clear but as he drew Lindegaard, he also dragged his shot wide of the far post.
It mattered little, as his side held on for a famous victory.
Norwich (4-4-1-1): Ruddy; Whittaker, Bassong, Turner, Garrido; Snodgrass (E Bennett 90), Tettey, Johnson, Pilkington; Hoolahan (Howson 83); Holt (Morison 83). Subs: Bunn (g), Jackson, Tierney,
Manchester United (4-4-2): Lindegaard; Rafael, Ferdinand (Anderson 83), Smalling, Evra; Valencia (Scholes 69), Carrick, Giggs, Young; Hernandez (Welbeck 69), Van Persie. Subs: Johnstone (g), Jones, Anderson, Cleverley, Fletcher. Booked: Rafael.
Referee: A Taylor (Cheshire).