It capped a wild year for Federer, one that began with him in tears after a five-set loss to Nadal, but included his first French Open win (and the career Slam that came with it), a return to the winner's circle at Wimbledon and the birth of his twin girls. I'm very happy about today. I nearly could have.
Anderson's huge serve kept Federer on the back foot and the towering eighth seed also fared much better than expected in the baseline rallies. He could have ended things right then and there.
It took almost five hours for the match to go final, somehow longer than Anderson's day with Federer. Disturbed by noises from the crowd, and a plane flying overhead, with the first break of the 5th set, Anderson made no mistake with his service game.
The comeback was just beginning.
Nishikori, who had won only two matches in 15 meetings with the 12-time major victor, broke for 1-0 in the fourth but was broken straight back.
That initial burst gave Federer 34 successive sets won at Wimbledon, equalling his own record set between 2005 and 2006. It looked like it would be five when Federer had a match point in the third set, while leading by two sets to none. But there was more.
Is there anything Roger Federer can't do?
Kevin Anderson (8) narrowly defeated Gael Monfis in four sets to reach the quarterfinals.
Roger Federer lost to Kevin Anderson in the quarter-final of Wimbledon 2018.
But having taken time to rediscover his best tennis, the former world No 1 has been in fine form at the All England Tennis Club and saw off Kei Nishikori to make his first semi-final at the tournament since 2015. There is still more tennis to be played. He made it to the the US Open final previous year, and he's firmly established himself as a top-10 player. He's the top seed and playing like it, winning sets that are close and others where he's simply dominated every touch. You definitely thought Federer would get the job done. "You're never really safe".
Anderson held his nerve with his relentless and powerful serve win the fourth and send the rip-roaring contest into an unlikely fifth and deciding set. The Swiss lost his serve, putting the match in Anderson's big-serving hands. The 32-year-old African is the highest-ranked player from South Africa.
Next, it was Nadal's turn to engage in a marathon match when he outlasted Del Potro on Centre Court.
Federer was playing on Court One for the first time in three years, but the 20-time Grand Slam champion denied his surprise move from Centre Court was a factor.
Anderson's next opponent will come Friday against No. 9 seed John Isner, who made his first ever semifinal with a win over Milos Raonic. Nadal will advance to play in his sixth Wimbledon semifinal, and his first since losing in the finals in 2011.
The 12-time Slam victor prevailed despite picking up two code violations and accusing umpire Carlos Ramos of "double standards".
Federer was completely out of sorts by now and his uncharacteristic struggles on his forehand didn't improve in the fourth set.
Later, Ramos warned Djokovic for a time violation, but that didn't seem to faze the Serb.
Djokovic will play Nadal in the semifinals. "As of right now, I'm sort of more focused on that than getting too excited about the overall picture".
"I don't think it really mattered, to be honest", he said.