The fifth-seeded del Potro failed to convert four match points when serving at 5-4 in the fourth set, but maintained his composure to close out the contest with his first opportunity in the tiebreaker that followed. He played well in the latter two sets of his four-set triumph over Kei Nishikori - a match that lasted "just" 158 minutes - and created 14 break point chances in 17 return games.
Another player who needed a decider was Rafa Nadal, as he squeezed past Juan Martin Del Potro to land us a victor from our recommended bet, but the after-effects of these arduous wins for Anderson and Nadal may not help them in their quest to reach Sunday's final. "In some ways he deserves to go through too", Nadal told the BBC after the match.
"The last set had a little bit of everything, great points, great rallies, he was hitting insane with his forehands". "I've tried to build the momentum and I've been very pleased with the way I've been playing in the grass court season". "It's a day to be happy".
Even then he was left flat on his stomach as his racket went flying out of his hand.
"Rafa is a fighter and he has a fantastic game".
Victory secured, Nadal climbed over the net and ran over to the baseline to help the distraught Del Potro back to his feet.
"I'm trying to get to where he's already been", said Isner, who has won all 95 of his service games this fortnight, thanks in part to a tournament-leading 161 aces.
The Argentine next faces two-time champion Rafael Nadal, who has reached the Wimbledon quarterfinals for the first time since 2011.
"He deserved to win today".
"After nearly five hours match, I fell down". "I don't want to stop here. But Rafa came to me and we shared a big hug, and it was kind of him".
It's going to be the usual for the 32-year-old - an ice bath and lots of work with his physio.
For Djokovic, he can claim a 13th major title - placing him just one Slam behind Pete Sampras - and a fourth Wimbledon crown, which would leave him behind only Bjorn Borg, Sampras and Federer in the Open Era standings.
It was not as if Nadal was playing badly.
"Of course I was anxious when I lost the second set, no?"
It was as if that out-of-the-blue news threw the Spaniard off his stride and he fluffed his lines to drop his serve.
Del Potro fought back, but Nadal held again after the former wasted a break point.
'Winning a Grand Slam gives a lot to these players like (Roger) Federer or (Novak) Djokovic. The powerful Argentinian has won five of his 15 matches against Nadal but lost to the world number one at two of the last three slams.
John Isner and Kevin Anderson will play in their first Wimbledon semi-final on Friday.
While it's probably less likely you'll share a name with Swiss ace Federer, those who do are being offered a meal for themselves and one friend.