That mishap could not stop Nadal from reaching his sixth Wimbledon semi-final and he celebrated the moment by raising both arms up into the skies after four hours and 48 minutes of thrilling action.
Friday's other semi-final pitches Anderson, the eighth seed who lost to Nadal in last year's US Open final, against ninth-seeded American John Isner.
Djokovic will need all that belief, however, as he has not faced anything yet at Wimbledon of the level of Nadal. "Anything could happen", Nadal said.
The pair have produced some of the greatest matches ever seen - which include memorable Grand Slam finals and career-defining victories.
World number one Nadal, the 2008 and 2010 champion at the All England Club, trails Djokovic, the 2011, 2014 and 2015 victor, 26-25 in a rivalry which began at Roland Garros 12 years ago. Yeah, honestly it's not easy playing Novak because I don't have good records. It is always a big test. He was playing, you know, good tennis again.
"I think she said, "I'm sorry", Bertens said.
He showed signs of recovering at the French Open before a shock loss in the quarter-finals against unseeded Italian Marco Cecchinato, then reached the Queen's final where more mental fragility proved his undoing against Marin Cilic. That gave me really trouble.
"I will try to hold my service games most of the time. Obviously I've been very pleased with the way I've played so far on the grass court season".
Nadal's total of nine Grand Slam match-wins against Djokovic is the most that anyone has managed against the Serb, but Djokovic has also defeated Nadal at the Grand Slams more often than anybody else, with 4 victories against the Spaniard at the majors.
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.
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.
Del Potro finished with 77 winners to Nadal's 67 but could not convert any of his five break points in the fifth set.
A fearless effort from Isner but it is Anderson who will reach the final.
However, both men have grown into the tournament while Federer crashed out to big-serving South African Kevin Anderson.
Federer suffers shock Wimbledon quarter-final loss to Anderson The two-time Wimbledon champion will face Djokovic, a three-time victor at the All England Club, for a place in Sunday's final.