Nadal had had his right knee taped during his gruelling third-round clash against Karen Khachanov but insisted afterwards it was not a big issue and he appeared in good shape for his next two matches.
Nadal, bidding for a fourth title in NY and 18th major, had spent the best part of 16 hours getting to the semi-finals.
Nadal's challenge looked doomed even as early as the first set, as he was feeling the injury after just four games, he admitted.
"It's not a tennis match when one is playing and the other is at the side of the court". "As you can imagine, it's very hard for me to say goodbye before the match finished", Nadal said afterwards, the news outlet reports.
Only Ivan Lendl and Pete Sampras have been to the NY decider as often as the remarkable Serb, who lost on his last visit two years ago, to Stan Wawrinka, and has won twice, against Roger Federer in 2015 and Nadal in 2011, the best season of his career. After losing the first three matches of his comeback this year, he has gone on to reach the quarter-finals at Roland Garros, lose to Nadal in the semi-finals in Rome and in the Queen's final to Cilic, before beating Kevin Anderson in the Wimbledon final.
"I'm having two great years", added Nadal, who was trying to complete a French Open-US Open double for the second straight season. Incredible. I mean, I have to take at least 10 shirts for every match.
After the third game of the second set, he had a medical timeout so the trainer could massage his right leg and once again apply tape.
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Salah's strike in last December's Merseyside derby also makes the shortlist, with FIFA.com users voting for the victor . Since then Real Madrid have won it three times on the trot with Ronaldo very much orchestrating those successes.
Japan's Kei Nishikori meets Novak Djokovic of Serbia in Friday's second semi-final with a spot in the final against Del Potro on the line.
But Nadal was unable to take advantage and immediately after the time-out, with the 32-year-old struggling to cover the court, Del Potro broke again.
He has resurrected his career impressively after minor surgery on his long-term elbow injury, which kept him out of the game for six months past year.
Djokovic's most recent win over him was in the quarter-finals at Wimbledon this summer, on his way to winning the title.
Thankfully, the 21st seed appeared to avoid injury and duly played his best tennis of the match after dropping the first set, fighting hard to stay with his illustrious opponent.
"He's a big match player and I'm sure the final will be a thrilling match". In the final when I beat Rafa and then Roger I was a kid then, but now I am much older'.
Should he win on Sunday, he will equal Sampras' record of 14 Grand Slam titles.
Djokovic and Del Potro have faced each other 18 times before with the Serb leading the head-to-head 14-4.