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.
A set littered with one lengthy rally after another, eventually went to Nadal on serve, finally giving him the match.
After claiming the first set by a single break, Nadal lost the next two by tight margins as Del Potro stole the show on Centre Court with acrobatic shot-making and a total of 33 aces behind his serve.
Nadal, 32, bounced about like the long-haired teenager in the sleeveless top who first played here 15 years ago, as hungry for a third Wimbledon title as he was for his 11th at Roland Garros a month ago.
Next up for the Spaniard is a blockbuster last four showdown with Novak Djokovic. He picked himself up and dusted himself down to play on for another eight games, but it was a different story an hour later when there was nothing left to fight for. It had a little of everything, great points, great rallies, he was hitting insane with his forehands. It also meant the "King of Clay" was one game away from taking the set.
Del Potro, saved four set points and grabbed one of his own on Nadal's serve and levelled at a set apiece, winning the breaker 9-7.
Nadal ended the four hour and 48 minute thriller with a backhand volley victor past a lunging Del Potro who ended the contest lying flat on his stomach.
Del Potro let two break-back points slip in the sixth game and then forced Nadal to save three more breaks for 5-3.
Del Potro too noted the change in conditions but appeared to relish the chance to slide around a bit more on the grass.
While you were watching the World Cup semi-final last night, and before that, while you were desperately trying to get out of work to go home and watch the World Cup semi-final, there was a day for ages playing out at Wimbledon, featuring, of course, Roger Federer and Rafa Nadal.
Nadal caught Del Potro napping in the fifth game of the fourth set, breaking him to love to lead 3-2. Only negative thing is I played nearly five hours, and I had the chance maybe to play less winning that second set.