Ole Gunnar Solskjaer was the victim of a footballing massacre in Manchester after suffering his darkest hour at Old Trafford.
Solskjaer and his spineless United flops were left with faces as red as their shirts following their biggest hammering since 2011.
United had been reduced to 10 men before half time, but this had little bearing on the eventual outcome.
The day had started with the news Edinson Cavani had jetted into Manchester to undergo a medical ahead of a free transfer to United.
But part of the medical should have included him having his head examined – because the Uruguayan striker must be mad to even contemplate joining a team that now concedes goals for fun due to its defence being nowhere near the standards expected or required at this level.
If one game showed how skewed United’s priorities in the transfer market have become, it was this one. United need new defenders, not ageing forwards past their best.
The back four Solskjaer sent out here still cost a staggering £198m – but all it could produce was a disasterclass in defending, to be torn to shreds by a ruthless Spurs outfit who made it an ecstatic return to Old Trafford for Mourinho.
Those who thought Mourinho would return to his old club to ‘park the bus’ in the hope of getting a point were seriously mistaken.
The Premier League has been raining goals since it began again last month and here was another example of how good, solid defending appears to have become a thing of the past.
Spurs gave United a goal start after just 24 seconds when Davinson Sanchez tripped Anthony Martial from behind to concede a needless penalty before Mourinho had even had time to take his seat in the dugout.
Bruno Fernandes made no mistake to give United the perfect start, but their joy was very short lived as Spurs hit back with a vengeance to score twice in three minutes and leave the home side stunned.
United’s defending was shambolic from start to finish and it took Spurs just four minutes to take full advantage when a mix-up between Harry Maguire and Luke Shaw allowed Tanguy Ndombele to steal in and smash the loose ball past De Gea to make it 1-1.
It was the start of a collapse that will haunt Solskjaer for months to come.
Three minutes later Maguire felled Kane, who picked himself up to take the free kick quickly and send Son racing clear of the flat-footed Eric Bailly.
Son beat De Gea with ease and when Martial saw red following a clash with Erik Lamela, United were in self-destruct mode and dire straits.
Before the Frenchman had even got in the showers, Kane finished another superb attack with a clinical finish to make it 3-1 after Spurs ripped through United’s powderpuff defence again.
Mourinho punched the air in delight, because he knew the game was over as a contest.
It had become a damage limitation exercise for Solskjaer’s men, but his sorry bunch couldn’t even manage this.
Son made it 4-1 eight minutes before half time, Serge Aurier added a fifth on 51 minutes and Kane hit United for six from the penalty spot on 79 minutes to complete a rout that will leave Solskjaer and his bosses facing serious questions once again.