It was deeply fitting Amad Diallo should decide this Manchester derby, mainly because for long periods he seemed to be the only person on the pitch not playing under heavy sedation.

Footballers are often said to have stood out in a game. Diallo stood out here mainly because he actually seemed to like playing football. In the event this expressed itself in four extraordinary minutes during which Diallo played a lone hand in turning 1-0 down into a 2-1 win. Even before that there were long periods during which the slight, speedy, jarringly urgent figure on the right side of Manchester United’s attack appeared to be the only person on the pitch with any kind of hope that life can still go on, like the lone survivor in a George Romero movie, out there haring around a shopping centre dodging zombies.

The greatest beneficiary of Diallo’s energy and craft is his manager, who went out on a limb here from the start. For Ruben Amorim this was one of those occasions in a hugely outcome based sport where the finest details can change an entire narrative. The biggest thing Amorim did here was to drop Marcus Rashford from his squad. The second biggest thing was to talk about it before kick-off, telling the TV cameras this was a choice based on attitude and commitment, in effect an all or nothing act of scythe-swinging directed at his most famous home-grown star.

“I pay attention to everything, the way you eat, the way you put your clothes on to go to a game,” Amorim said, which probably didn’t come across as intended. As this game ticked past 70 minutes, with United 1-0 down and still playing haunted, lateral, meandering football, those quotes was already being crowingly reproduced on the internet. United boss watches players get dressed. Rashford axed for eating fish course with wrong knife. That kind of thing. Football hates a vacuum. Something is needed to fill the empty air. Ridicule will do, and often ridicule can turn out to be terminal.

At which point, enter: Diallo, and the triumph of hope. United’s equaliser on 88 minutes came after a terrible back-pass from Matheus Nunes, fed through to Diallo, who saw in his periphery the onrushing Nunes, siren blaring, bent on rescuing his own mistake. His skill in that moment was to wait, to put a foot on the ball, to let Nunes run straight through him. Bruno Fernandes buried the kick.

City were paddling hard towards the end of the pool by now, sinking slowly, arms aching. Diallo just kept running. With the 90 minutes up he galloped on to a lofted pass from Lisandro Martínez, nicked the ball past Ederson, who really does love a random cartwheel, and clipped it into the far corner. Even then Josko Gvardiol could have sat down on the ball, but instead tried and failed to back-heel it away.

Football does at least seem to have retained its acerbic sense of humour. The most startling aspect of Diallo’s intervention was the utter deathliness of the game that had preceded it. Watching these two teams wander around aimlessly, elite football as reimagined by a robot with a hangover, it was amazing to think of the vast and baroque superstructures that had given birth to this spectacle, the tiers of micro-management, the billions spent, the teams of lawyers in a death wrestle off stage, the nation state will to power.

At the end of which these two global sporting entities produced a game that was for long periods like watching someone unload a dishwasher badly.

Forty minutes in Kyle Walker was guilty of a ludicrous piece of play-acting, collapsing on to his back after brushing against Rasmus Højlund’s forehead. Maybe Walker just wanted feel something. Crash into me Rasmus. Make me bleed. Let’s do some fake pain.

Otherwise this was dead air football, off-cuts, spasms of trapped energy. City still looked like a team with something soft and muddled at its centre. Luckily, they were facing opponents who seemed afraid to press too hard.

City duly took the lead on 36 minutes with a header from Gvardiol after a deflected cross, enabled by some terrible faux-defending. Even after that, and outside those final four minutes this felt like a missed opportunity for United and for Amorim. City were there for the taking. They just are these days. Fernandes produced a ragged, wholehearted version of his best self. Højlund was game and willing, even if at times it feels a bit like watching a very eager riderless horse that still thinks it’s going to win the grand national.

But in the end it was Diallo and the simple refusal to give up that changed the day. He now has six assists and two goals in his past nine games.

Whatever happens from here Amorim will always be grateful for Diallo’s intervention, for those four minutes that will buy just little bit more of the patience he asked for, but was never really likely to get. Time is currency for Amorim. He got a little more here. He got to make a statement of his own ruthlessness. Small wins for now. But this version of Manchester United will feast on them.