Riding an implausible wave of retro romance, Roger Federer, 36 and in sight of his third slam title of the year, foundered on the sharp rocks of hubris on day 10 of the US Open when Juan Martín del Potro ripped up his invitation to a semi-final against Rafael Nadal.

Instead, the big man from Tandil will be Nadal’s opponent on Friday. The world No1 leads him 8-5 over their careers, but only a brave bookmaker would make either of them a clear favourite. Earlier, Nadal, a two-time New York champion, was at his commanding best in dismissing the limp but fevered challenge of the Russian teenager, Andrey Rublev, 6-1, 6-2, 6-2. That, though, was not a reliable guide to what awaits the Spanish clay-court supremo on Friday.

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Del Potro, his mighty forehand clicking like a rifle, deserves to be there after winning 7-5, 3-6, 7-6 (8), 6-4 in two hours and 50 minutes under the roof on Arthur Ashe, and Federer might one day regret his pre-match dismissal of the Argentinian’s victory over him in the 2009 final here. If it played any part in his downfall, only the winner will know but, from the outside, it did not look to help Federer’s cause.

Del Potro was 20 back then and has done heroically well to beat wrist injuries and the usual fluctuations of form over the past few years to even be in the mix here. Eight years ago, the world was his. As Federer conceded this week, he might well have gone on to be No1. But he surprised many in his critique this week on their final that year.

“I left that match with a lot of regrets,” Federer said, after both of them had reached the fourth round this time in vastly contrasting styles. “I should have been up maybe two sets to love or ... two sets to one. The only time when he was really better, in my opinion, was the fifth set. Obviously that was good enough to beat me that day. I had a great run... but it ended my five-year reign here in New York. But Juan Martín did play extremely well. I felt like he deserved it at the end.”

Rarely has someone been damned so completely with faint praise. And Del Potro, fresh – or at least reheated – from his efforts to come from two sets down in seeing off Dominic Thiem, was fired up from the start. If he needed an incentive, Federer had supplied it to him in words. He dug in to take the first set, and a tremor of concern rippled around the stadium among the Federer faithful – as well as those American TV pundits who were torn between craving a Federer-Nadal semi-final (in their first ever meeting here) or the extension of the Del Potro fairytale.

From love-3 down in the third set, Federer found enough magic to get to a tie break. And this is where the match pivoted in Del Potro’s favour.

A set apiece, Federer changed ends 4-2 up with the ball in hand. Del Potro challenged an ace and won the point. Del Potro’s right arm was grooving, but the net got in his way. Federer had the set on his racket at 5-4. Del Potro hit long; set point. Del Potro saved when Federer unwisely served to his forehand then levelled with a huge serve wide. Mirka smirked in the box, and smiled when Del Potro double-faulted. Husband stepped up – but he put a backhand wide for 7-all. He grabbed another set point. Del Potro crushed a forehand for 8-all, and was at the net to grab set point, his first, with a volley. Federer volleyed long on the backhand. Job done.

As they slugged it out in the fourth set, it took del Potro five games to make the breakthrough. Federer’s racket oozed a weird mixture of familiar certainty and anxiety. He knows no other way but to go for his shots, and not enough of them stayed legal as Del Potro moved to within two holds from victory.

As Federer served to stay in the tournament, Del Potro, 5-3 up, thrashed an outrageous forehand past Federer’s whiskers at the net before the Swiss held with a whizz-bang backhand that kissed the line. This was high-grade theatre.

Now it was Del Potro’s match to lose. They had been playing two hours and 45 minutes. The crowd, remarkably, seemed to be equally divided. They wanted more drama, certainly, but the hunger for a denouement was greater.

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Del Potro clipped the baseline with an ambitious forehand for 15-love. He aced for 30-love. He dumped a backhand volley: 30-15. At the end of an attritional rally, he hit long for 30-all. The crowd went crazy. Federer put an ambitious forehand volley madly wide: match point. A huge Del Petro serve forced Federer to block a set-up return and the Argentinian belted the gimme down the line, lifted his arms to the sky in exultation.

As Federer slipped away, thwarted but valiant, the stage belonged to Del Potro.

“It’s hearwarming, he’s an amazing young man,” John McEnroe told his ESPN audience, while simultaneously expressing regret that Federer and Nadal are unlikely to ever meet here.

Del Potro said courtside: “I think I played my best match of the tournament. I did everything well. I served well and I deserved to win.”

“I think it’s my court too,” he said, when asked about Federer’s dominance here in the distant past. Addressing the crowd, he said, “You make me feel happy every time I play here. I love to see you shouting for me. And I guess the crowd will be tough for me against Rafa. I think I got lucky in the tie-break, double fault at 6-all. But I made a good return. In the first set I played even better.”

He then addressed the large and vocal Argentinian gathering in Spanish, which roughly translated as, “Thank you from the bottom of my heart.” That is a heart with almost bottomless reserves.