Seldom can such a ravishing goal have had a more rotten postscript. By the final whistle, Marcus Rashford hardly resembled a figure who had conjured one of the great strikes of any Manchester derby. That faraway look was back, as he sloped down the tunnel to another bitter United reckoning. An unfortunate ending, yes, but it was not just City’s three second-half goals that clouded his mood. After all, he had followed his wondrous hit with two fluffed chances, triggering his replacement by Antony with 15 minutes left. Truly, he is the perpetual enigma.

With Rashford making way, the TV cameras zeroed in instantly on Gareth Southgate here in the Etihad stands. The juxtaposition was not accidental: the winger, once a shoo-in to start for his country, has been rendered a squad member at best by his recent travails, creating a dilemma for an England manager who has stood by him. His problems were thrown into sharp relief by the performance of Phil Foden, his international team-mate. Where Foden was consistently radiant for City, Rashford’s light shone only fleetingly.

Even before he sent United fans into delirium with one elegant swipe of his right boot, Rashford had delivered a pointed rebuke to his many critics. “If you back me, good,” he declared. “If you doubt me, even better.” This was the less-than-subtle subtext to his celebration, as he hared off towards the away end and pointed his finger at his temple as if to highlight his psychological strength. Except the glow of vindication could not last.

Before he knew it, Rashford was put through with a priceless opening to double United’s advantage – absurd though that might have been in the context of City’s dominance – and badly fluffed his lines. Unleashed through the middle, he failed, while still absorbing the euphoria of the breakthrough, to bring the ball under control, allowing the danger to be cleared. Just before City drew level, he had a second opportunity to counter-punch, finding himself with only Kyle Walker to beat. The response was half-hearted as, toe-to-toe with the fastest player in the Premier League, he crumpled in a heap.

Although Rashford was adamant he had been clipped, reviews proved less conclusive. Erik ten Hag did plenty of protesting on his behalf, earning a booking for his trouble and reflecting later: “Maybe soft, but there was contact.” From there, United’s scorer all but vanished from the picture, suffering the indignity of being substituted by Antony, the £85 million passenger who surely counts among the club’s worst signings of the past 25 years. The manager insisted there were extenuating circumstances, explaining how both Rashford and Jonny Evans had been chosen for this derby despite carrying injuries.

Sometimes, you wonder if it is helpful for Rashford to be offered immediate mitigation. His first-person article last week, headlined “Who I Really Am”, smacked of somebody who was struggling to cope even with justified critiques of his attitude on the pitch, which has drifted into indolence on occasion. “My family turned down life-changing money so I could wear this badge,” he bristled. Roy Keane, the type of United captain so desperately needed to arrest the club’s slide into dysfunction, was notably unimpressed with that comment.

“I wouldn’t be happy hearing about the sacrifices he has made, the money he has turned down,” Keane said, after a United display that underscored that glaring gulf with City. “He’s doing OK. A lot of fans who go to games week in, week out, are all saying the same thing, so maybe Marcus has to reflect, to think, ‘Maybe there are some times when I’m not closing people down’. There are high expectations because of the last couple of seasons, where he has scored lots of goals. United want to see more of it. Sometimes, you do need to take a closer look at yourself. There’s nothing wrong with wanting improvement.”

By Keane’s standards, it was emollient. This was not the lacerating ferocity he once reserved for Harry Maguire and David De Gea when he deemed them less than fully committed to the United cause. He seemed genuinely to care about Rashford, to recognise that amid the garish headlines about the Belfast party and the Carrington car crash, a rare talent is still trying to negotiate the pitfalls of fame.

Besides, anyone who observed United’s late collapse against City would agree that Rashford is far from their No 1 headache. His struggles can be seen as the symptoms of his club’s wider malaise, where lapses into mediocrity are too easily tolerated and where a perennial irritant like Bruno Fernandes is somehow considered a viable heir to Keane as captain.

Rashford does not deserve any renewed pillorying after this result. He produced a goal that leapt straight into the canon of derby-day marvels, even if it was fated to be a footnote to defeat. What was frustrating, though, was that this masterstroke prefaced some all-too-familiar mistakes. United are desperate for Rashford to become the figure who makes a decisive difference. Instead, he is cast as somebody who flickers exhilaratingly into life – and then fades maddeningly away.