NORWICH City won at Old Trafford for the first time in over 26 years as goals from Cameron Jerome and Alex Tettey earned them a memorable victory.
United dominated the opening half an hour but City snatched the lead when Jerome finished off a counter attack seven minutes before half-time.
Tettey's intelligent finish on 55 minute had the Canaries' vocal supporters dreaming of a first away win against the Red Devils since August 30, 1989.
Anthony Martial pulled one back for the home side, but they eventually slipped to their third defeat on the spin.
After City's improved performance in the second half against Everton last weekend, Alex Neil stuck with the team who featured in that 45 minutes.
That meant Ryan Bennett returned to start in central defence alongside Sebastien Bassong, with captain Russell Martin shifted to full-back.
Wes Hoolahan started an away league match for the first time in nearly three months, while Ireland compatriot Robbie Brady was included against his former employers.
United welcomed back skipper Wayne Rooney from injury for his 500th appearance in their colours.
The home team dominated the ball in the opening period of play with their attacking trio of Rooney, Memphis Depay and Anthony Martial all seeing plenty of possession early on.
Rooney had the ball in the net on the ten minute mark, but Marouane Fellaini, playing off the England striker when United were attacking, was flagged offside in the build-up so the goal was ruled out.
Depay and Rooney each then missed the target - the Dutchman's effort coming from outside the box after City had failed to clear their lines, while Rooney's was presented to him after a strong run by Juan Mata.
Alex Tettey dragged City's first opening wide on 21 minutes, but Neil's side were losing the battle in the middle of the park meaning that they had little stranglehold on the game.
United forced several corners but the Canaries' defensive pair of Bennett and Bassong were doing well, and the home crowd's frustrations increased.
City then had a better spell that culminated in Hoolahan winning free-kick off Mata in a promising area, but Martial was on hand to head clear Brady's set-piece on 36 minutes.
Then, seven minutes before half-time, another counter-attack yielded a surprise opening goal for Neil's men as Redmond found Jerome, who saw off the challenges of two defenders before finishing beyond De Gea.
The tension in the air at Old Trafford was palpable as once again they saw their side fail to capitalise on dominance - on the contrary, the Yellow Army were in fine voice as they celebrated their team's advantage.
HALF-TIME: Manchester United 0-1 Norwich City
United continued to look uncertain at the back at the beginning of the second half, even though they saw most of the ball once again in the early exchanges.
Ten minutes after the restart, the City supporters were sent into delirium when another counter-attack saw their team add a second.
Jerome turned provider this time as he slotted a through ball into Tettey's path, and the midfielder scored a rare goal by poking the ball past De Gea from the edge of the area.
It left United, who hadn't lost at home in the league this season, with a mountain to climb - Louis van Gaal responded by replacing Fellaini with Ander Herrera with half an hour left to play.
Neil responded by introducing the energy of Jonny Howson for the flair of Hoolahan, but before the former Leeds man had had a touch, van Gaal's side had pulled one back.
Ashley Young swung a cross in from the right, and Martial wriggled free from defenders before firing the ball into the roof of the net.
That allowed United to build up a head of steam, but when Young required some treatment with 20 minutes left on the clock, it offered a welcome moment of relief for the Canaries.
Mata had an opportunity to test Rudd when Martin fouled Martial 20 yards out - Rudd was up for the challenge, pushing the Spain international's set-piece away.
Neil made two more changes to help his team see out the final ten minutes, and it worked as they held on for a sensational three points.
FULL-TIME: Manchester United 1-2 Norwich CityGOALS
: Red Devils
: Anthony Martial (66) - Canaries
: Cameron Jerome (38), Alex Tettey (55)
: De Gea, Young, Jones, Smalling, Blind, Carrick, Fellaini (Herrera 60), Memphis, Mata, Martial, Rooney (c). Subs not used
: Romero (GK), Borthwick-Jackson, McNair, Varela, Schneiderlin, Pereira.
: Rudd; Martin (c), Bennett, Bassong, Olsson; Redmond, O'Neil (Mulumbu 82), Tettey, Brady; Hoolahan (Howson 66); Jerome (Mbokani 82). Subs not used
: Ruddy (GK), Whittaker, Dorrans, Odjidja.
: Michael Oliver
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