Shortly before 2.30pm, they got in through an entrance in the shadows of the Munich tunnel - a symbol of our club's tragic yet everlasting bond with the European Cup.
The Glazer family's criminal attempts to sever that tie with the preposterous European Super League was the cause of all this as a trickle - then a torrent - of fans smashed through Old Trafford's security defences to get on to the pitch - which is more that can be said for the players of United and Liverpool.
A planned protest which was supervised by a heavy presence of stewards and police ended up with fans on the playing surface kicking match balls amongst themselves, stealing corners flags, hurling flares at the Sky Sports TV gantry and ultimately saw clashes with police outside the ground.
There must have been more than a thousand, gathered in front of Old Trafford in time for the 2pm protests with the eyes of the world on this small corner of Salford ahead of the most high profile game on the English football calendar.
There was nowhere near the 10,000 that had been predicted, but there was still a significant number and, ultimately it was enough to force an unprecedented postponement.
Fans arrived from both ends of Sir Matt Busby Way, past the now obligatory anti-Glazer banners and the men adorned in the gold and green - the colours of United's original incarnation - Newton Heath.
Some came with young children - a strong message that here was a protest for all ages but one that would seem very inappropriate come the end of the carnage.
Fans congregated around United's Holy Trinity - George Best, Bobby Charlton and Denis Law - immortalised in bronze in front of the Megastore. Old Trafford had sat dormant and silent for over a year with fans watching the matches from home amidst the Covid pandemic, but had now come alive again.
The first chants went up with more than a hint of menace but - still - everything remained peaceful.
"Joel Glazer's gonna die" went up as red smoke from the flares drifted across the forecourt to the thin cordon of police stationed in front of the entrances.
"How we kill him I don't know, how we kill him I don't care, all I know is Glazer's gonna die".
A smattering of camera crews filming the protests were showered with beer (now that I don't condone - what a waste) - as the numbers grew and emotions began to run high.
A couple of loud bangs signalled the official start of the protest and fans immediately began moving towards the stadium, edging towards the steel gates of the Munich tunnel and just a matter of yards from where United's hierarchy would normally file through to their seats.
More flares and further chanting as those at the front pulled and wrestled with the locked gates, eventually smashing down a door in the south-west corner - a door normally used for medical reasons.
There seemed little resistance from the army of police and stewards, indeed so easy was it to outmuscle them and get through their defences that it made you wonder if they were in on it or, indeed, happy to assist.
Many fans got on the pitch through the disabled section whilst others slid down the tarpaulin and climbed over seats to get on the pitch. Some jumped on the goalposts and one man was knocked clean off the bar by another protester curling an inch perfect 20-yarder into the top corner.
By now things were turning increasingly ugly with a flare launched in the direction of Sky's outdoor studio housing TV pundits Micah Richards, Roy Keane and Graeme Souness.
At a time when Covid-free bubbles around footballers and coaching staff have been vital to the Premier League playing on throughout the pandemic, it had now become a nightmare for both clubs and the authorities.
A major security breach had put the match in serious jeopardy.
Half an hour later, the pitch invaders emerged victorious at the rear exit to Old Trafford, hurried on their way by security and applauded every step of the way by fans who had gathered there to try and block the team buses from getting in.
Some more returned to the hallowed turf after kicking in the glass door to the disabled access lift, returning to a hero's welcome, serenaded as they marched back through the gates 40 minutes further on.
A police van and eight more officers were deployed there to ensure the safe arrival of the team buses that would never arrive as the United players watched the drama a short distance away from the sanctuary of their hotel rooms at the Lowry.
By now, things had invariably turned nasty. You always get idiots and, at the front entrance to Old Trafford, demonstrators had been drinking for several hours and started to hurl bottles and even metal security barriers at the police whom - up until then - had been very restrained.
Perhaps too much so. A police helicopter only appeared halfway through the protests and, despite the large number of Tactical Aid Unit vans, the officers were not wearing body armour or helmets. Faced with an increasingly unruly mob and a force under siege, the police advanced in two lines with batons drawn to split the protesting throng in half and forcing them back down Sir Matt Busby Way in opposite directions.
The fans reacted angrily while others - including members of the assembled media - were caught in the carnage. More bottles were thrown and skirmishes broke out at both ends of the road as two separate stand-offs developed.
The only person left behind by police was a one man band ploughing a lone furrow in front of the Holy Trinity statue.
Undeterred by the chaos from all sides, the man played You are my Sunshine - in homage to United boss Ole Gunnar Solskjaer - on a saxophone even if he had to compete with the noise of the helicopter overhead and hundreds of empty bottles and cans blowing the wind in front of him.
It was a bizarre image - perhaps only matched by one of United's corner flags being carried off down the road - to end the strangest of days.