No 3 del Potro will now 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. The negative thing is two of them have been in the quarter-finals and semi-finals of a grand slam, close to fight for titles.
"I didn't know if I (would) be a tennis player again or not".
"Well of course it's not the best way to win a match". It was established as the surprise theme of his career just months after his sensational upset of Federer in that 2009 US Open final. Nadal said. "It was just one player playing, the other one staying on the other side of the court".
The Serb's favourable record against Nishikori will give him great belief that he can make it through to an eighth final at Flushing Meadows and with the temperatures set to cool down in NY, that will only help his cause.
Earlier, Nadal showed signs of distress nearly from the start as he limped noticeably after a gruelling 69-minute opening set.
That effort took its toll with the Spaniard twice needing to have his right knee bandaged before calling it a day after the conclusion of the second set.
The finalists appear to be in good health, although they will be as exhausted as any player would be after six matches in a fortnight.
"I've been fighting with many, many problems to get [to] this moment", del Potro said. "I didn't tonight. He played maybe 80 percent of the game to my backhand, and there was the advantage for him".
Novak Djokovic expresses frustration with team during match
The Australian also suffered with the heat, having to disappear off court at 2-2 in the second set to change his sweat-soaked kit. He fended off seven break points but couldn't stop Djokovic from converting on the eighth to take the two-sets to one lead.
It was odd enough to see a player be allowed to do that during, instead of after, a set, but even odder for it to happen after an even number of games, rather than at an odd-game changeover.
The game started on an ominous note for Nadal as del Potro broke his serve in the first game of the first set.
But the big Argentine swept through the tiebreaker, wrapping up the opener after 69 minutes of impressive shot-making.
The Spaniard had called the trainer onto the court after the seventh game of the opening set and had his knee taped.
Nadal was trailing Juan Martin del Potro by two sets down, before calling it quits. There's also that five-set semi-final match at Wimbledon in 2013 to consider: Del Potro doesn't seem to get awed by Djokovic, or by the big stage. Djokovic also has won nine straight major semifinals and will play his 23rd final on Sunday - the third most in men's tennis history behind Roger Federer (30) and Rafael Nadal (24).
Serena Williams will play for her record-tying 24th Grand Slam singles title after advancing to the U.S. Open final with a 6-3, 6-0 victory over Anastasija Sevastova. "I had my biggest memories on the tennis court playing on this court ... but I was a kid". Then I think it was a little bit better.
Del Potro won his one and only Slam, so far, at the US Open in 2009.
In front of him on Sunday is a man who has beaten him 14 times in 18 contests and in all four of their slam matches.