Serbia's Novak Djokovic jumped three spots to third after he captured his third US Open title and 14th overall grand slam.
On Sunday, No. 3 del Potro will face No. 6 Novak Djokovic, who advanced with an emphatic 6-3, 6-4, 6-2 victory over No. 21 Kei Nishikori in the second semifinal.
Del Potro was leading 7-6 (3), 6-2 after two hours of play when Nadal shook his head and said he had to stop.
All four players have reached the U.S. Open final while only Nishikori hasn't won it to make this the first Grand Slam final four since the 2012 Australian Open in which all four players were past finalists.
The defending champion and No. 1 seed at Flushing Meadows recovered from his disastrous start and other stumbles along the way to beat No. 9 Dominic Thiem.
The No.1-ranked Nadal overcame a shaky start and used his customary relentless style to wear down No. 27 seed Karen Khachanov physically and mentally.
Murray hadn't played in a Grand Slam tournament since Wimbledon last year, before needing hip surgery that has limited him to just eight matches this year.
The top in both the WTA and ATP rankings remain unchanged with all the players holding on to their spots.
The Swiss maestro had won five titles in a row in Flushing Meadows and was a game away from a sixth in 2009 when Juan Martin del Potro pulled out a fourth-set tiebreaker, then won the fifth set.
The top-ranked Nadal beat the unseeded Greek upstart 6-2, 7-6 (4) for his fourth Rogers Cup crown and fifth victory of the year. He has 33 ATP World Tour Masters 1000 titles.
Rafael Nadal rallied at night to join the Greek teenager Stefanos Tsitsipas in the semi-finals.
Nadal, playing for the first time since a five-set loss to Djokovic in the Wimbledon semifinals, topped France's Benoit Paire 6-2, 6-3 at night after a series of rain delays.
Nadal will now look to bounce back in the Rogers Cup, a build-up to the US Open where he will be defending his title.
Nadal said it was "an exceptional circumstance" that he has remained on top of the tennis world after turning 30, alongside Federer, 36, and Djokovic, 31.
That trio has combined to win 10 of the past 14 championships at Flushing Meadows: Five for Federer, three for Nadal, two for Djokovic.
Djokovic sent the strongest signal yet he is back at the top of tennis by reaching his fifth Wimbledon final with a 6-4, 3-6, 7-6 (9), 3-6, 10-8 victory over rival Rafael Nadal.
They had played on and on, through 6 1/2 hours of ho-hum hold after ho-hum hold, during the second-longest match in the history of a tournament that began in 1877.
Rafael Nadal won 7-5, 6-7 (7), 4-6, 6-4, 6-4 on Wednesday and earned a trip to the semifinals at the All England Club for the first time since 2011.
Roger Federer, Serena Williams and Rafael Nadal have reached the quarter-finals of Wimbledon.
The top-seeded Halep's exit means only one of the women's top-10 seeds remains in the tournament, Pliskova, which leaves Serena Williams as the big favourite to win her eighth Wimbledon title.
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