Juan Martin Del Potro came back from two sets down and saved two match points to beat No 6 seed Dominic Thiem in the men’s singles last 16 in the best match of the US Open so far.

The 24th seed, cheered on by a large Argentinian contingent on the Grandstand court, won 1-6, 2-6, 6-1, 7-6 (7-1), 6-4.

Despite feeling ill and requiring treatment, he came through in 3hr 35min to set up a quarter-final against Roger Federer. The Swiss No 3 seed beat Germany’s Philipp Kohlschreiber 6-4, 6-2, 7-5.

Federer, 36, struggled with a back injury in the build-up to the tournament and left the court after the second set for a medical timeout.

‘I just needed a bit of a rub on my back. Or my … bottom,’ he said on court afterwards. He later added: ‘I just felt something, sort of my muscle being tight at the back. Sort of my quad, I guess.’

After needing five sets to win his first two matches in New York, Federer made it back-to-back three-set wins.

The 19-time Grand Slam champion did not face a single break point over the course of 1hr 50min. The five-time champion produced another impressive performance, but for once the spotlight was elsewhere as Del Potro’s comeback gripped Flushing Meadows.

The noise from the 8,000-seater Grandstand court outstripped that from the 24,000 spectators on Arthur Ashe Stadium as Del Potro saved two match points with thumping aces, on his way to setting up a rematch of the 2009 final he won against Federer.

‘I played one of the epic matches of my career here at the US Open, which is my favourite tournament, in front of a great crowd,’ the Argentinian said. ‘I was thinking to retire in the middle of second set because I couldn’t breathe, I couldn’t move well, and Dominic was dominating the match so easy.’

Russian teenager Andrey Rublev knocked out Belgian ninth seed David Goffin to set up a quarter-final with Rafael Nadal.

Rublev, 19, won 7-5, 7-6 (7-5), 6-3 to become the youngest man to reach the last eight at Flushing Meadows since Andy Roddick in 2001.

Nadal, 31, saw off Ukraine’s Alexandr Dolgopolov 6-2, 6-4, 6-1 in 1hr 41min.

In the women’s draw, Karolina Pliskova cruised into the quarter-finals with a straight-sets win over American Jennifer Brady.

The Czech world No 1 had to save a match point before beating China’s Shaui Zhang in the third round, but she needed only 46 minutes to win 6-1, 6-0 on Arthur Ashe Stadium against the world No 91, who was competing in the last 16 for the first time.

Pliskova will now face American 20th seed Coco Vandeweghe in the next round.

Vandeweghe beat 2015 French Open finalist Lucie Safarova 6-4, 7-6 (7-2). They were joined in the last eight by Estonian qualifier Kaia Kanepi, who beat Russia’s Daria Kasatkina 6-4, 6-4 to reach her first US Open quarter-final since 2010.

The 32-year-old will face fourth seed Elina Svitolina or Madison Keys, seeded 15th, next.

Photo: Matthew Stockman/Getty Images