And in the next round, Mark Robins. Football has found itself assailed in recent years by states, oligarchs and private equity, the concentration of resources at a handful of clubs in a tiny number of western European countries destroying the balance that once sustained it, the potential of its soft power meaning that it has been preyed upon by regimes desperate to launder their image and secure influence. But, despite all that, the sport has retained its mischievous sense of humour.

It was Robins who scored the winner for Manchester United against Nottingham Forest in 1990 that saved Sir Alex Ferguson’s job, carrying them through the third round of the FA Cup to initiate an exhaustingly dramatic campaign that culminated in the trophy. At the end of his fourth season in the job, that was Ferguson’s first silverware at Old Trafford, the herald of 23 years of almost constant success.

Robins has a fine record as a lower-league manager. If Coventry win their game in hand in the Championship, they will be one point off the promotion playoffs and, on Saturday, they scored twice in injury time to beat Wolves in their own astonishing quarter-final. Robins has only faced United once before as a manager, in 2009-10 in the League Cup when his Barnsley lost 2-0. But on occasion, football has an impeccable sense of timing: of course he should pop up again now, just as everybody is talking about Erik ten Hag having enjoyed his Robins moment.

In truth what happened at Old Trafford on Sunday was far more dramatic than United’s win at Forest 34 years ago. The latter game has been rather polished by myth, a performance of grim defiance won with a header 11 minutes after half-time. Only context made it memorable. Sunday’s 4-3 win over Liverpool was a victory for the ages, the sort of game that will stir the soul of United fans for ever.

It felt a game out of time. Players in the modern age don’t look quite so exhausted as they did on Sunday, dragging their limbs forward for just one more assault, socks round ankles, hair soaked with sweat, cramp gnawing at their calves. Modern teams do not usually end up with an injured forward hobbling around at centre-back. Trying to work out the United formation by the end was impossible: Harry Maguire and Diogo Dalot were the only two defenders left, and yet Maguire kept popping up in the Liverpool box.

These were two sets of players living entirely in the moment; nobody was keeping anything in the tank for the internationals to come. There was no settling for penalties, just relentless, end-to-end attacking. From United’s point of view, it was a victory in the best traditions of Matt Busby, rooted not in tactical schema or clever counter-pressing but in individual effort.

A Robins figure was unexpected – and, therefore, given the FA Cup’s nature, entirely predictable. Amad Diallo was brilliant at times on loan at Sunderland last season, repeatedly skittering in off the right flank, a waif, apparently too fine for the Championship until he unleashed his left foot: a weapon, despite his physical slightness, capable of whipping balls with extraordinary velocity and accuracy. His winner away at Birmingham was one of such preposterous quality the only reasonable response was to laugh, the goal at Wigan not far off.

Injury has hampered his return to United and, operating in his favoured right-sided role, Alejandro Garnacho has been one of the few positives for United this season. But, still, there has been an element of frustration that Diallo’s involvement has been limited to four substitute appearances this season when United would not let him stay at Sunderland for another year.

It would be misleading to suggest Sunday showed he can fit in a Ten Hag system because what happened had little to do with structure. What Diallo did show, though, was that when the game becomes chaos, he has the heart for the fight. It was he who won the ball back and then, when he had taken Garnacho’s pass at the edge of the box, had the wherewithal to shape on to his right foot. Conor Bradley checked – but Diallo only uses his right foot if there is no option. He let the ball keep rolling, opening up the angle and then, with Caoimhín Kelleher perhaps also momentarily deceived by the drop of the right shoulder, squeezed his shot just inside the far post. A mishit, some said, and it wasn’t the cleanest strike, but it was good enough, the cleverness of the finish lying in the way he had contrived a way to use his stronger foot.

Will it be enough to keep Ten Hag in the job? Perhaps, perhaps not. To an extent what matters is less what United do next – although if they were to go on to beat Manchester City or Chelsea in the final, it would be hard to oust him – than that, amid the sort of ecstasy that can make years of underachievement seem worthwhile, United have enjoyed a win over their greatest rival that will resonate for decades. At the very least Sunday ensured that if Ten Hag is dismissed in the summer, he will not pass unmourned.

This is an extract from Soccer with Jonathan Wilson, a weekly look from the Guardian US at the game in Europe and beyond. Subscribe for free here. Have a question for Jonathan? Email soccerwithjw@theguardian.com, and he’ll answer the best in a future edition