Five-time champion, Roger Federer produced another impressive performance, but for once the spotlight was elsewhere as Del Potro’s comeback gripped Flushing Meadows.

Juan Martin del Potro came back from two sets down and saved two match points to beat sixth seed Dominic Thiem in a raucous US Open classic to book a place in the last eight battle with Federer.

The 24th seed, cheered on by a large Argentine 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 three hours and 35 minutes to set up a quarter-final against Roger Federer.

The Swiss third 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.

“I just didn’t want Philipp to wait. It was more precaution. It’s all good. No problems there. I’m not worried about it. I’m sorry I had to do it.”

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 Argentine 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.”

The 28-year-old was broken in the first game and seemed to be struggling with his eyesight.

Having lost the first set in 36 minutes, and after receiving medical treatment, the former champion trailed 6-1 3-0 and finally hit his first winner in the 12th game, but then wasted three break point opportunities.