Nadal saved three break points before an imperious forehand victor put him 5-3 up and he put away a simple volley to finally finish off Del Potro, then made his way around the net to embrace his tired opponent as he lay on the court following another tumble.
The other matchups see defending champion Roger Federer against Kevin Anderson; Novak Djokovic takes on Kei Nishikori and Milos Raonic meets John Isner in a matchup of big servers. "You know that you can't win against him if you don't play very well". I tried to resist and maintain focus. At two sets to one down, the prospect of Nadal and Federer exiting a grand-slam tournament on the same day for the first time was becoming real.
It also followed a semi-final defeat to Nadal at the French Open last month where he won just seven games.
"Very happy, a very important achievement for me to be back in the semi-finals of Wimbledon".
Djokovic came into the Championships on the back of a frustrating year which was blighted by an elbow injury and saw him slide down the world rankings as a result.
Djokovic has the slight edge at overall Tour-level at 26-25, but Nadal ended a seven-match losing streak against the Serb at Madrid past year and also won their only meeting so far in 2018 in the semi-finals of the Rome Masters.
"I play Los Cabos in Mexico - the beach", he smiled.
Del Potro trails Nadal 10-5 in head-to-head meetings - his five wins all coming on hardcourts.
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The IT tech said that the divers were not heroes and directed attention to the rest of his team and the Thai Navy Seals. Volanthen and fellow Brit Rick Stanton were the first rescuers to find the boys deep in the Tham Luang cave complex.
Second, his opponent will be two-time Wimbledon champion Rafael Nadal.
Nadal lost only eight points behind his serve in the opening set, but Del Potro needed only one break point to take a 5-4 lead in the second.
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But Nadal was first to break in the deciding set and he built a 5-3 advantage with a looped forehand victor before confirming his final four place with a volley after four hours and 48 minutes.
"I said at the beginning of the tournament, getting through to the quarters was a big goal of mine", he said.
Isner, 33, will be playing in his first major semi-final and is bidding to become the first American man to reach a Slam final since Andy Roddick finished Wimbledon runner-up in 2009. "That's all I got for you right now".
"If I want to beat him (Nadal)", Del Potro said.
"I just kept on telling myself I have to continue believing".