Amad Diallo seals Manchester United’s late derby turnaround win to stun City

When Ruben Amorim oversaw his previous victory over Manchester City – with his old club Sporting in the Champions League – it was to push the reigning Premier League champions towards crisis. That was in early November and it was City’s third defeat on the spin.

As Amorim repeated the trick, it was to pep up his new project at Manchester United and leave Pep Guardiola on his knees. There seems no way out of the misery for the City manager, this an eighth defeat in 11 matches in all competitions, the decline of his all-conquering team stark and extraordinary.

For so long, it had looked as though City would close out a much-needed win thanks to Josko Gvardiol’s header following a 36th minute corner. They were meek and uncertain throughout, lacking basic oomph but United had no cutting edge. They were powder-puff in the final third. And then, at the very end, they were not and they could embrace a result that Amorim will seek to use as a touchstone.

Related: Pep Guardiola feels he is ‘not good enough’ after City’s late defeat to United

It was Amad Diallo, the standout performer of Amorim’s fledging tenure, who made the difference. Playing in the right-sided No 10 role, Diallo was quick and direct but above all, he refused to believe that defeat was his destiny. He kept on running, ever alive to possibility and, after he had won the penalty for 1-1 – converted by Bruno Fernandes with two minutes of regulation time to play – he ran some more.

Working off Matheus Nunes and in between Gvardiol and Rúben Dias, he reached a high ball from Lisandro Martínez on the bounce and the first touch was a wonderful piece of improvisation, lifted up and to the side of the advancing Ederson. He followed it up with a volley from a tight angle that squeezed home, Gvardiol failing to clear from in front of the line.

Nunes, playing as an emergency left-back, had conceded the penalty after leaving a pass intended for Ederson woefully short. Diallo nipped in, moving away from the goalkeeper and he had the presence of mind to pause and trick Nunes, who had raced back, into a rash challenge. Where was the game management from City?

Diallo has contributed six assists in the league this season – he does not get one in the official statistics for winning a penalty – but the goal, his fourth in all competitions, was the real jaw-dropper, the one that furthered the sense of helplessness that has come to grip Guardiola and City.

The game had been framed to a certain extent by Guardiola opening up on Friday about the notion of losing the dressing room. Imagine hearing that towards the end of October when City were unbeaten in all competitions. For the record, he has not lost the players. There was also the detail about his diet. He is sticking to soup in the evenings because his stomach is churning so much. The insecurities are everywhere and they bubbled during a slow-burn derby that – Diallo apart – was low on quality.

Amorim’s idea was to be solid; hence Noussair Mazraoui and Diogo Dalot as the wing-backs, Diallo in the more attacking position. The headline team news was the exclusion of Marcus Rashford and Alejandro Garnacho from the matchday squad, a decision that Amorim indicated was based on what he had seen from them around Carrington, which sounded ominous.

United could sense there were spaces in behind City’s defensive line and Manuel Ugarte got Diallo clean though in the 26th minute only for him to drag wide. The offside flag did go up. But they were rocked by Gvardiol’s goal, which had not been advertised. That it came from a corner was both sickening and unsurprising from a United point of view; they have routinely failed to defend properly from them all season.

City played it short and there was fortune when Kevin De Bruyne’s cross deflected off Diallo to loop up for the run of Gvardiol. But Dalot did not do enough while Rasmus Højlund got sucked towards the ball. Gvardiol was free to direct the header.

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Injuries were a part of the story. Guardiola was without Manuel Akanji and Nathan Aké while John Stones was fit enough only to return to the bench. With Rico Lewis suspended, the manager had only three fully available defenders; Maybe seven in the squad is not enough? It was why he turned to Nunes at left-back, with ultimately disastrous consequences. United would lose Mason Mount after 12 minutes – a bitter blow for the luckless midfielder.

There was controversy after Gvardiol’s goal, Kyle Walker going forehead-to-forehead with Højlund after he had fouled the United striker. Walker wilted to the ground, a shameful attempt by the 93-cap England international to get his opponent sent off. Both were booked.

United had rhythm and structure to their passing moves but they had to show greater personality and incision. City, meanwhile, were just happy to have something to hold in the second half. They invited United on and if it was weird to see them in such passive mood, creating so little, perhaps they reasoned United did not have what was needed to hurt them.

Diallo extended Ederson with a header and Fernandes had a massive chance on 74 minutes after he was released by Højlund. When his dinked finish drifted wide and Mount’s replacement, Kobbie Mainoo, got underneath a free header, United looked set to fall short. Diallo had other ideas.