Watford ramped up the pressure on Ole Gunnar Solskjaer to new levels with a deserved 4-1 win over a shambolic Manchester United at Vicarage Road - and it was a defeat that soon cost Solskjaer his job.
United's loss was their fourth in their last five games, and their heaviest to newly-promoted opposition in more than 30 years. Despite such a magnitude of defeat, Solskjaer - who was loudly booed by the away support at full-time - said he believed "we can turn this round" after the loss, which leaves United 12 points off leaders Chelsea after as many games.
But on Sunday morning, United announced that Solskjaer had been sacked.
Goalkeeper David de Gea, one of the few - or only - Manchester United players to emerge from the defeat with any credit, described the loss as "embarrassing" and "unacceptable", and apologised to the club's fans.
De Gea added: "It was hard to watch the team playing like today. I think it's a nightmare, after a nightmare, again, for a long time, so it's not acceptable.
"The players are trying to give our best, to fight for the team but for sure something is very wrong."
United could easily have been behind inside six minutes after Scott McTominay's clumsy foul on Josh King gave Watford an early penalty, but Kiko Femenia's goal on the rebound from Ismaila Sarr's saved spot-kick was ruled out for encroachment, and Sarr was again denied by De Gea from the retake.
Watford did not have long to regret their missed opportunity. Emmanuel Dennis teed up former United trainee Josh King to prod home (28) as the hosts pressed home their dominance, and Sarr doubled the advantage a minute before the break with a powerful finish.
Donny van de Beek, whose name had been cheered by the United fans for long periods of the first half, was introduced at the break and made an instant impact, nodding home from Cristiano Ronaldo's flick five minutes into the second period.
But United's discipline would again let them down again as Harry Maguire dented any hopes of a comeback when shown a second yellow card for a late challenge on Tom Cleverley after being caught in possession.
In injury time, goals from Joao Pedro and Emmanuel Dennis piled yet more misery on the visitors as they sunk without trace, in a capitulation perhaps worse than recent defeats to Liverpool and Manchester City, and one which would provide the final straw for Solskjaer's reign at Old Trafford.
Watford: Foster (7), Femenia (7), Nkoulou (7), Cathcart (6), Masina (7), Cleverley (7), Sissoko (7), Louza (8), Sarr (7), Dennis (9), King (8).
Subs: Hernandez (6), Ekong (7), Pedro (7).
Manchester United: De Gea (6), Wan-Bissaka (2), Lindelof (4), Maguire (3), Shaw (4), McTominay (5), Matic (3), Sancho (5), Fernandes (5), Rashford (5), Ronaldo (5).
Subs: Martial (4), Van de Beek (6), Dalot, Lingard (n/a).
Man of the match: Emmanuel Dennis
United fall to new low as Watford revel in rout
With a two-week break to forget about their collective club woes, Manchester United's players were given a rapid reminder of their lingering issues with six minutes gone as Bruno Fernandes' skied clearance fell for King, who was bundled over in the box by McTominay.
Sarr's penalty saved by De Gea and turned in by Femenia on the rebound, only for VAR to order a retake for encroachment - from which Sarr again was denied by the resurgent goalkeeper's excellent stop.
That chaos set the tone for a shambolic first half from United, who only once forced a save out of Ben Foster and instead saw De Gea beaten twice by a Watford side whose intensity, desire and gameplan they were nowhere near matching.
King was denied by a last-ditch Maguire block from a corner as the hosts began to ramp up the pressure and moments later found a way through, as Aaron Wan-Bissaka's poor header fell for Dennis to tee him up for a simple finish.
The ex-United youngster should have haunted his old club for a second time when nodding Adam Masina's cross straight at De Gea, but Watford would grab the goal they deserved before the interval as Sarr, who had looked nervous after his earlier penalty miss, shook off any self-doubt to take Femenia's cut-back emphatically.
The sight of Van de Beek warming up at the interval was met with the away end's biggest cheers of the afternoon, and five minutes after his introduction they were raised up another level as he headed in Ronaldo's unselfish assist from Sancho's cross.
For the first time, United had their tails up and looked dangerous, sensing an opportunity in behind Watford's backline, and only a number of tight offside calls stopped them working Foster more.
Ronaldo believed he had brought the game level before he was denied by another late flag, but having come so close United then undid any good work as Maguire was shown a second yellow card for catching Cleverley after his own heavy touch.
That proved the end of United's hopes of a comeback, and they never threatened after the red card. Instead, the hosts compounded their misery with a quickfire double in added time, as Pedro's effort squirmed through De Gea's legs before Dennis' fine finish across the goalkeeper sent Vicarage Road wild.
Solskjaer faced the visiting fans at the full-time whistle and when his approach was met by a chorus of boos, Bruno Fernandes indicated the United support should blame his team-mates instead of the manager - but there was only one man who would carry the can for such a dismal defeat, with United confirming his sacking on Sunday morning.
What now for Manchester United?
Sky Sports' Paul Merson: "This is the biggest club in the world but it's three and a half years without a trophy. I'm not the manager's biggest fan, but l am not liking what l am seeing from the players. It's a hard one because they are going to Villarreal in midweek. But can you go to Villarreal without a manager?"
Tim Sherwood on Soccer Saturday: "This was a lesson in desire. Manchester United had no team. They were just a bunch of individuals thrown onto the pitch. Watford absolutely destroyed Manchester United. This is an embarrassing result for Manchester United. Nobody is scared of playing Man Utd anymore."
What the managers said...
Watford boss Claudio Ranieri: "We were very good. The first half was amazing. We pressed a lot, made a lot of chances, and in the second half we suffered a lot, but that's normal against Manchester United. They wanted to draw, but a good thing for us was the red card. After that it was much better, we could close the spaces and create counter-attacks.
"I am speaking a lot about this kind of philosophy, I want to knock at the door and see which team I have in front of me. The players, slowly, understand my philosophy, how I want to play, and I'm very satisfied today."
Manchester United head coach Ole Gunnar Solskjaer: "I always have belief in myself, but at the moment it's a difficult time for us. I can trust every single one of them to give what they have, but the results are difficult. I believe we can turn this round.
"I am working for and with the club. Of course we have a good communication and if the club are thinking of doing something that is a conversation between us."
Man of the Match - Emmanuel Dennis
Despite not joining the list of Watford scorers until second-half injury time, Dennis was the Hornets' most dangerous attacking outlet up to that point, making King's opener and providing Sarr the ball for what should have been their second.
The Nigerian has blown hot and cold since arriving at Vicarage Road in the summer - he was on boiling form to put United to the sword.
Opta facts: Historic United defeat to promoted opposition
- This was Manchester United's biggest league defeat against a promoted side since September 1989, and a 5-1 loss against Manchester City at Maine Road.
- Watford have won back-to-back home league games against Manchester United for the first time.
- Only in 2001-02 (11 games) have Manchester United conceded 20+ goals after fewer games in a single Premier League campaign than they have this term.
- Josh King's goal for Watford was his fifth Premier League goal against Manchester United, with the Norwegian only netting more in the competition against Everton (8).
- Manchester United keeper David De Gea has saved the last two penalties he's faced in the Premier League, the same number that he'd managed from his previous 31 faced in the competition.
- Donny van de Beek's goal was just his second in the Premier League for Manchester United, with his first also coming as a substitute on his debut in the competition in September 2020.
- Harry Maguire was sent off for the first time in his Manchester United career, on what was his 121st appearance for the club in all competitions.
Watford travel to Leicester a week on Sunday, due to the Foxes' Europa League involvement; kick-off at 2pm.
Manchester United face a crucial Champions League trip to Villarreal on Tuesday night; kick-off at 5.45pm.