Norwich City heaped the pressure on Louis van Gaal with a 2-1 victory over Manchester United at Old Trafford on Saturday.
Cameron Jerome scored for only the third time in the Premier League this season to put the Canaries in front on 38 minutes and Alexander Tettey doubled the visitors' advantage nine minutes after the interval with another goal on the counter.
Anthony Martial's 66th-minute strike threatened to ignite a famous United comeback but it did not materialise as Norwich held on for their first victory at Old Trafford since 1989, Van Gaal's men being booed off.
The results see Norwich climb out of the relegation zone on to 17 points while defeat for United - their first at home in the Premier League this season - sees them fall out of the top four on goal difference and drop nine points behind leaders Leicester.
The afternoon began with Sir Bobby Charlton presenting Wayne Rooney with a commemorative plaque ahead of kick-off to mark his 500th appearance for the club.
And the United captain, reinstated following an ankle injury, looked to have capped his landmark day with an early goal, only for the linesman to rule his 10th-minute effort out for offside.
Rooney was arguably United's biggest threat in terms of goalscoring chances, but his dragged effort did little to concern Declan Rudd in the Norwich goal on 15 minutes.
Rooney's attempts to turn provider on 28 minutes saw Memphis Depay thwarted by Russell Martin's last-gasp intervention, before Marouane Fellaini and Chris Smalling failed to convert Daley Blind's corner from close-range a minute later.
That marked a turning point for the Canaries as they hit United on the counter to break the deadlock seven minutes before half time.
The bright Nathan Redmond slipped Jerome in behind the United defence where he skipped inside Ashley Young's rash challenge before calmly beating De Gea to become only the second opposition player to score in the league at Old Trafford this term.
Despite trailing, the United faithful produced a raucous reception for their team as the half-time whistle sounded. But this did little to inspire their side as Norwich went two up on 54 minutes.
United failed to learn from Jerome's opener as he turned provider, playing a one-two with Tettey on the break as he unerringly drilled the ball beyond the stricken De Gea.
The introduction of Ander Herrera momentarily sparked United into life, and they clawed themselves back into the game on 66 minutes.
Young's wicked cross from the right fell kindly for Martial and the 20-year-old, named Europe's best young player of 2015, showed flawless close control to cut inside Ryan Bennett and Sebastien Bassong before rifling the ball home.
The expected United revival did not materialise, though, as Norwich restricted the hosts to aimless crosses into the box before only a smart save from De Gea prevented substitute Youssouf Mulumbu from making the three on 83 minutes.
Smalling almost snatched a point at the death with a close-range header but it would have been cruel on a Norwich side deserving of the three points.
Tony Cottee's Soccer Saturday verdict
"United started off well; the crowd were right behind them. It was a good atmosphere but they spluttered the whole game.
"I think a lot of the money spent has been wasted. There's a lack of confidence without a doubt. Martial has too much responsibility on his shoulders. He's a 19-year-old kid who's been told to lead the line. There's no [Javier] Hernandez, [James] Wilson to make that simple tap-in. I do fear for Manchester United.
"I think it will come [Van Gaal's sacking] if they don't get the results. Manchester United as a football club are normally pretty loyal, stood by Sir Alex, and gave David Moyes as long as possible. Personally I wouldn't [keep Van Gaal in charge] but they have two big games now."
Man Utd: De Gea (6), Jones (6), Smalling (7), Blind (7), Young (5), Carrick (6), Fellaini (5), Depay (5), Mata (6), Martial (7), Rooney (6).
Subs used: Ander Herrera (6).
Norwich: Rudd (7), Bennett (7), Martin (7), Bassong (8), Olsson (6), Tettey (8), O'Neil (7), Redmond (8), Hoolahan (9), Brady (6), Jerome (8).
Subs used: Howson (7), Mbokani (6), Mulumbu (6).
Man of the match: Wes Hoolahan.