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After all this was at 24-all in the fifth set of a Wimbledon semi-final that had been going on for what seemed like forever but was in fact well past the 6-1/2 hour mark.
But not only did Anderson jump back to his feet, the South African astonishingly switched his racket into his left hand and, gripping it half way up the handle, hit a forehand to get the ball back and take the point before he broke and then went on to win the match. It was that kind of a bonkers contest.
It was that kind of ingeniousness that was needed to break the serve-hold-serve-hold deadlock that went on for almost three hours in the deciding set alone as Anderson became the first South African man in 97 years to reach the Wimbledon final.
History books will show that Anderson came out on top in a 7-6(6) 6-7(5) 6-7(9) 6-4 26-24 epic that lasted six hours and 36 minutes - the longest ever semi-final at Wimbledon - but those numbers fail to illustrate the astonishing feats of endurance shown by the two gladiators on the most famous stage in tennis.
It is a match that featured 102 thunderbolt aces, 264 unreturned serves and 247 bone-rattling winners but none of those will stand out as much as the heart and desire of the two combatants as both tried to reach to a first Wimbledon final.
When Isner finally slapped a weary forehand wide at 7.46pm local time, there were no wild roars, no fist pumping and no raised arms in celebration from Anderson.
All the 32-year-old had left in him was to give Isner a sympathetic hug after he came out on top in the second-longest match ever contested at the All England Club.
"I don't know what to say right now. Just playing like that in those conditions was really tough on both of us. At the end you feel like it's a draw, but someone has to win," an exhausted Anderson, who had sensationally beaten defending champion Roger Federer in another nail-biting five-setter two days ago, said.
"John is a great guy and I really feel for him. If I was on the opposite side I don't know how you can take that playing for so long and coming out short... getting through something like that is quite different.
"I have to recover as much as I can for the final now. It will take time to process it but I'm in the final of Wimbledon and that's a dream come true," he added ahead of Sunday's showpiece against Rafael Nadal or Novak Djokovic.
Playing Isner, who is enshrined in Wimbledon folklore for winning the "endless match" - an 11 hour five minute humdinger against Nicolas Mahut in 2010, was never going to be easy for Anderson as he had beaten the American only three times in 11 meetings and had lost five straight matches dating back to 2012.
A showdown between two tennis skyscrapers - with Isner topping the 6 foot 8 Anderson by two inches - predictably featured three tiebreaks.
With Anderson serving second in the final set and having to hold 20 times to stay alive, Nadal and Djokovic were left wondering if they would ever get on court for their semi-final.
However, soon after Djokovic had gone on social media to show he had been reduced to playing a game of marbles on the locker room floor - a message punctuated with three laughing emojis - Anderson delivered the knockout blow.
After watching Isner strike a weary forehand wide, Anderson advanced to the Wimbledon final at the 10th time of asking.
Brian Norton was the last South African man to reach the final in 1921. South African-born Kevin Curren contested the 1985 final but he had become a U.S. citizen by then.