At the beginning of last season, Erik ten Hag oversaw a 2-1 Premier League victory against Liverpool at Old ­Trafford to ignite his managerial tenure. Nobody had seen it ­coming after defeats in his opening two matches. It was like a fairytale.

It has soured somewhat this ­season, the difficulties piling up, but now this – another win here against Liverpool which few had predicted. In the heat of the moment, as a delirious United crowd looked ahead to an FA Cup semi-final against Coventry – who are managed, of course, by their former cup hero, Mark Robins – it felt like the result that could save Ten Hag.

He had needed a performance from his team as a bare minimum, for the players to show some personality; ideally a win, as well, to prolong their season because a Champions League finish via Premier League position looks unlikely (although on this ­evidence, who knows?)

Ten Hag got the lot as Liverpool hit the first real bump after ­Jürgen Klopp’s announcement in late January that he will step down as the club’s manager at the end of the season. The dream of a four-trophy send-off is over.

Liverpool played their part in an absolute thriller. They were the better team in the second half of normal time, looking to close out a 2-1 scoreline. Some of United’s players looked out on their feet. But that was when the craziness started.

You would have got long odds on the identity of United’s initial ­saviour. Antony has not divided opinion this season; there has been only one ­opinion about him. But there he was, on as a substitute, taking a touch after an incision from the indefatigable Alejandro Garnacho in the 87th minute, spinning and sending a low shot into the bottom corner. With his right foot, too – a sentence that practically demands an exclamation mark. Antony was excellent. He deserves the praise.

There was still time for Harvey Elliott, on as a Liverpool ­substitute, to float a cross against the far post and Marcus Rashford to blow a golden opportunity with the very last kick of normal time. When Rashford pushed his shot past the far post, having been released by the substitute, Christian Eriksen, there was not a United fan in the ground who did not have their hands on their heads.

Extra-time lurched one way and then the other. United were dominant and then Elliott produced the dictionary definition of a sucker punch, shooting from range and seeing the ball deflect off Eriksen to beat André Onana.

When Ten Hag introduced Mason Mount for Victor Lindelof in the 106th minute – it was Mount’s first action since November – he had only two recognised defenders on the field (Diogo Dalot and another substitute, Harry Maguire). He had switched to 3-2-4-1 in the 85th minute; now it was Antony on the left of the defence.

Back came United and after Maguire had shot straight at Caoimhín Kelleher, it had to be Rashford who supplied the equaliser to ­reinvigorate their belief. Not that it ever truly left them. This was the biggest detail for Ten Hag. It was Scott ­McTominay who played the final pass and ­Rashford did the rest.

McTominay would miss a great chance from a Rashford cross. Penal­ties loomed. And yet there was a final twist. Amad Diallo, yet another substitute, had played a part in ­Rashford’s goal, getting a foot to a Darwin Núñez pass to regain ­possession.

Now, with 120 minutes on the clock, his moment arrived. United won possession and broke through Garnacho. Inevitably. And when he went left to Amad, the winger threaded a low ­finish into the far corner. It was only his second United goal. Cue bedlam.

Amad had been booked earlier, a little harshly when Alexis Mac Allister blasted a quickly taken free-kick at him. He ripped off his shirt in the goal celebration to collect a second yellow card but nobody seemed to care; not the United fans who roared him off down the tunnel.

When the final whistle blew, Antony sank to his knees, head in hands, practically overcome and it was a vivid scene in many other areas. Certainly, there was much to process after a tie that had fired from the outset, United ­having opened with intensity, ­Kobbie Mainoo prominent in possession.

United scored first when ­Garnacho, after a smart run over and up the inside left of the area, unloaded a shot which Kelleher could only parry and McTominay had a ­tap-in. United had chances for 2-0, none ­better than for McTominay after a flash of twinkle-toed brilliance by Mainoo. McTominay shot too close to Kelleher.

Liverpool rallied. They thought they had equalised in the 37th minute when Mohamed Salah teed up Wataru Endo for a low finish, until Salah was ruled to have been fractionally offside. But Klopp’s team caught a break when Núñez laid off for Mac Allister, whose shot deflected off Mainoo to deceive Onana. Jarell Quansah had started the move with a striding run away from Bruno Fernandes and then Rashford; both United players had to do more defensively.

Liverpool completed the one-two punch before half-time of normal time when Fernandes was robbed by Joe Gomez on the right as ­Liverpool brought the press; the United captain wanted a foul but it was not there. He would be booked for dissent. When Gomez crossed, Lindelöf cleared only as far as Luis Díaz, who found Núñez. He cut inside and shot, Onana ­parried and Salah had a simple finish for his 13th goal in 14 matches against United.

It was easy to feel that United’s chance had gone when Liverpool took control after the second-half restart, hogging the ball, Núñez ­flickering with menace. It would turn into one of the classics between these bitter rivals.