Nishikori was handed a swift defeat at Arthur Ashe Stadium, losing 6-3, 6-4, 6-2 to the sixth seed.
And after the match Nadal's disappointment at having to quit was evident.
But trouble in this one seemed predetermined by the length of time the world's No. 1 was kept on the court in his five-set, tie-breaker quarterfinal victory over Dominic Thiem late Tuesday/early Wednesday. However, his worries here have been induced by the extreme heat, rather than the strain on his limbs and he appreciated the significant drop in temperature for his routine straight-sets win over Kei Nishikori in the second semi-final. Even for his iron strength, Nadal now 32, would have been feeling the fatigue.
He avenged his most recent last-four loss in NY - in 2014 vs. Nishikori, the only prior time they had met in Flushing Meadows. The Spaniard winced and limped in the second set. Nadal bested the Argentine in their meeting past year.
Juan Martin del Potro of Argentina during the semifinal match against Rafael Nadal of Spain. Djokovic, another player whose recent injury cost him time at the top of the tennis pyramid, won Wimbledon this year and is rounding into his elite form again. I have tremendous respect for him as a person and a player. I'm happy for that'. I am having a lot of success. But he made up for it in the tiebreak, winning 7-3, to put Rafael Nadal's bid for back-to-back US Open titles in jeopardy. "Like thousands of other tennis players around the world I'm trying to be the best I can be". "I know how tough is this thing".
He said: "I waited as much as I can".
Past year saw Roger Federer and Rafael Nadal share the slams and return to their former glories.
Del Potro is no stranger to injury. When I played Roger nine years ago, he was the favorite to win as well.
The No. 1-seeded Nadal has a history of tendinitis in his knees and he said he felt a problem in the right one early in the first set. People pulled for returning star "Delpo" as much as they did for the defending champion. The match was off to a competitive start as the players traded breaks in the first two games of the match.
And this looks to be the Serb's year if he can convert a second slam of the season. That shows the quality that he has, especially in the big matches.
The surgeries, like it or not, will be a constant footnote in del Potro's story. And while he still had the devastating forehand that's been one of tennis' signature shots and carried him to the 2009 title, repeated wrist injuries had made him one dimensional on the backhand side. He had the trainer attend to his troublesome knee again, got his quads massaged and threw frustrated glances at his team box.
As his opponent limped increasingly heavily between points, Del Potro ruthlessly fired in winners, his backhand proving nearly as potent as his famously magnificent forehand.
"It means the world to me". It was so hard for me to keep playing, I was in too much pain. Nadal, who had beaten Del Potro en route to the title a year ago, struggled mightily with his movement as he camp sat quietly watching. That was followed by three procedures on his left wrist, which sidelined him for 2 1/2 years' worth of Grand Slam tournaments.