The moment that a turned a difficult task into a mountain to climb arrived in the 41st minute.
Ruud van Nistelrooy slid a delightful pass into the path of Paul Scholes who tumbled over after making contact with Mauricio Taricco. Referee Mike Riley initially gave nothing but as he waved away appeals, his assistant waved his flag.
He clearly signalled penalty, Taricco was sent off and van Nistelrooy almost took the net off with his penalty kick. 2-0, 10 men, 45 minutes to go.
Until then, we had more than held our own in terms of possession and football played.
With a strong wind playing havoc we started brightly as both Teddy Sheringham and Gus Poyet forced Fabien Barthez into action.
But United took the lead with their first incisive move after 16 minutes. David Beckham, sprightly as ever down the right flank, played a ball into van Nistelrooy, took the return pass in his stride and drilled his shot into the bottom corner from 15 yards.
Neil Sullivan then saved well from Roy Keane but we refused to allow United to settle and were soon playing our football again, unfortunately with little reward in terms of chances.
Play remained in midfield for most of that time until the penalty decision that totally changed the complexion of the game.
Glenn Hoddle acted swiftly and introduced Les Ferdinand in place of Sergei Rebrov at half-time, bravely electing to stick with two up front when many teams might have opted for one up.
It almost paid dividends straight away as Ferdinand headed Davies' deep cross into the air and as the defence backed off, he was left unmarked but smashed his volley into the stands.
United were always going to create chances and Diego Forlan, making his first start for United, should have opened his account but missed two golden chances after 53 and 55 minutes.
The third goal arrived after 63 minutes, another clinical finish. Forlan broke down the left flank, van Nistelrooy controlled his cross and laid the ball back to Beckham who had time to control, take aim and fire ferociously into the top corner.
Sheringham volleyed Sherwood's clever dink just wide but number four soon followed. Sullivan parried Keane's cross and van Nistelrooy pounced, sold two defenders by faking to shoot with his left foot before slotting home with his right.
Keane almost got in on the act when he tricked his way past Richards and flashed a shot wide from the angle.
Forlan continued to miss chances left, right and centre, Sullivan saved well from Keane and denied Beckham his hat-trick.
In fairness, no-one shirked the hard work or their responsibilities - epitomised when Ferdinand went in for a 40-60 with Barthez - but, in reality, it was all over with the wave of that flag.
It could be argued that Manchester United are the last team that needs an extra hand, not least at Old Trafford, but they got that thanks to a willing assistant referee on Wednesday night.