Manchester United were briefly reduced to nine men during their 3-0 defeat to Tottenham Hotspur thanks to a substitution mishap which summed up a humiliating afternoon at Old Trafford.
The Red Devils crumbled to a miserable loss which piled further pressure on manager Erik Ten Hag as goals from Brennan Johnson, Dejan Kulusevski and Dominic Solanke handed Spurs a fourth consecutive win in all competitions.
With the away side on top just before half-time, Bruno Fernandes was sent off for a tackle on James Maddison which gave United a mountain to climb to get back into the contest.
To make matters worse, England midfielder Kobbie Mainoo hobbled off injured just moments later as the wheels began to fall off for Ten Hag's outfit.
At one point United were reduced to nine men after they appeared to miscue the substitution protocol, leaving replacement Mason Mount stranded on the sidelines.
Manchester United were briefly reduced to nine men during their 3-0 defeat to Tottenham Hotspur thanks to a substitution mishap
The home side appeared to miscue the substitution protocol, leaving replacement Mason Mount stranded on the sidelines
United's woes worsened as Kobbie Mainoo went off injured and they struggled to get Mount on
The play had restarted before the former Chelsea man had a chance to get onto the pitch with the home fans booing in frustration at the farcical mishap.
When the ball finally went dead, Mount entered the fray but the midfielder was later replaced himself after an injury left blood pouring from his head.
The chaotic first-half incident also saw Mainoo appear to complain to substitutes Antony and Casemiro about something with the two men in bibs looking on in bemusement.
The breakthrough in Sunday's clash, which continued a trend of early goals in matches between the two, had come from an unlikely source in the away side's back line.
Picking up the ball inside his own half, Micky van de Ven channelled the spirit of Franz Beckenbauer as he glided unchallenged down the left channel before beating three men as he arrived in the opposition box.
He then fizzed a delivery low across the home side's goal, which was met by a gleeful Johnson who tapped home. The finish continued the former Nottingham Forest man's rich vein of form and gave him a fourth goal in four matches.
He then nearly doubled his tally for the day after being found in bags of space by Kulusevski inside the United box, but the right winger's low strike crashed into the left-hand post.
Alejandro Garnacho then also struck the woodwork but it was all Spurs and the home side ressembled a group of ungelled individuals, as they so often have over the last few seasons and Fernandes's red card summed this up.
Bruno Fernandes was sent off for a tackle which scraped the shin of the James Maddison just before half-time
The dismissal gave United a mountain to climb at 1-0 down and with Spurs well on top
When the ball finally went dead, Mount entered the fray but the midfielder was later replaced himself after an injury left blood pouring from his head
The result mounted more pressure on Erik Ten Hag after a poor start to the season
By the time Mainoo trudged off, Ten Hag's side were desperate for half-time to arrive and when it did Spurs walked off the pitch with mixed emotions - a spring in their step after a free-flowing team performance but a sense of ruefulness after a host of missed opportunities.
But they need not have worried. Just over a minute into the second period, the away side repeated their speedy trick with Kulusevski scoring his first of the season.
Johnson turned provider as he bounded into the United box exploiting the bags of space which had become symptomatic of the home team's chaotic defensive shape.
He found Kulusevski in the area who poked it past Onana at full stretch before wheeling off in manic celebration.
An impressive double save from Onana saw Werner pass the ball straight at the keeper before the Cameroonian pounced to grab it from the feet of Solanke.
But these near-misses served to embolden United who creeped back into the game, backed by defiant fans who had braved the chilly and wet September weather.
Lisandro Martinez was at the centre of the action with the defender shooting wide and having a strike blocked as the Red Devils looked for an unlikely goal to halve the deficit.
Substitute Casemiro then almost silenced the critics of the last few weeks as he laced it past the post on the half volley with Spurs now creaking.
Tottenham Hotspur produced a free-flowing attacking display to condemn ten-man Manchester United to a crushing 3-0 defeat
Ange Postecoglou's side made it four wins in a row in all competitions and could have had six or seven
The away team scored early in each half to set the tone, Brennan Johnson finishing after a spectacular Micky van de Ven run in the first period
Any vague hopes of a miraculous comeback to save Ten Hag's skin were demolished with 13 minutes left on the clock as new signing Solanke bagged a decisive third.
Pape Sarr flicked on the ball from a corner and it fell into the path of the Englishman who poked home from just four yards out - his third goal against United in three matches.
Ten Hag remained motionless on the touchline as thousands of exasperated Red Devils supporters headed for the exits around him. Another day closer to a long-drawn out departure from the United hotseat.