LONDON -- Roger Federer was one point away from a rather tidy straight-sets victory in the Wimbledon quarterfinals. One point.
And then, slowly, over the next two-plus hours, all the way until the fifth set reached its 24th game, as the temperature dropped and the spectators' cries of "Let's go, Roger!" echoed through the shadows, everything came apart for the eight-time champion against an opponent who'd never beaten him before nor made it this far at the All England Club.
In a stunning turnaround in an unfamiliar setting -- No. 1 Court instead of Centre Court -- the top-seeded Federer blew a match point and, eventually, all of a big lead in a 2-6, 6-7 (5), 7-5, 6-4, 13-11 loss to No. 8 Kevin Anderson on Wednesday.
"It was just one of those days where you hope to get by somehow," Federer said. "I almost could have. I should have.
"... I'm up two sets to one. It's all good, so ... At that point I wasn't thinking of losing."
World No. 1 Rafael Nadal rallied to win a grueling five-set match against Juan Martin del Potro 7-5, 6-7 (3), 4-6, 6-4, 6-4 and reach the semifinals, where he will face a resurgent Novak Djokovic. Anderson will next face American John Isner.
Federer was leading by two sets and 5-4 in the third when, with Anderson serving, he got to match point. Federer managed to return a 134 mph serve, but on his next stroke, he shanked a backhand.
Back to deuce. From there, it all began to change. Anderson held for 5-all, broke to 6-5 with a violent return winner off a 97 mph second serve, then staved off three break points and closed the set with a 133 mph ace.
"I had my chances," Federer said, "so it's disappointing."
This was only the third time in Federer's 20 years of contesting Grand Slam matches -- 269 in all -- that he lost one after taking the opening two sets; both of the other defeats came in 2011. And, according to the ATP, it's the fifth time Federer lost a match at a major tournament after holding a match point, something else that last happened seven years ago.
"I just kept on telling myself, 'I have to keep believing.' I kept saying that today was going to be my day, because you really need that mindset taking the court against somebody like Roger," Anderson said. "If you go out there with doubts or unsure what's going to happen, like I maybe did a little bit in that first set, it's not going to go your way."
How hard was it to see this coming?
Federer was 4-0 against Anderson entering the day, winning every set they'd ever played against each other. But there was more. So much more. Federer was attempting to reach his 13th semifinal at Wimbledon and move closer to title No. 9, both of which would have broken his own records.
He came into the match having won 32 consecutive sets at Wimbledon, a run he stretched to 34, tying his own record, before faltering. And he had held serve 81 games in a row at the grass-court major, a streak that grew to 85 before Anderson broke him a surprising total of four times.
"I had moments where I was great ... other moments where I don't know where the hell I was moving to," Federer said. "I don't know if that was his serve. But I also have a feeling, it was a feeling of mine, you know, not getting it right.
"It's just not one of my best days, but they don't happen very often, either. It's one of those average days you have to try to win the match, and I just couldn't get it done today. So it's disappointing."
Not that Anderson is anything other than an elite tennis player. He was, after all, the runner-up at last year's US Open.
But he had never made it beyond the fourth round at Wimbledon until this week, carried by his booming serve. He hit 28 aces against Federer, saved nine of 12 break points and managed to hold his own in the rare lengthy baseline rallies.
"I think I had my chances, so it's disappointing," Federer said. "... He was consistent. He was solid. He got what he needed when he had to. Credit to him for hanging around really that long."
As the fifth set became as much a test of mental strength as anything, from 4-all to 6-all to 8-all to 10-all, Anderson was as steady as he needed to be. And it was Federer who blinked, double-faulting to face a break point at 11-all, then slapping a forehand into the net to cede the key break.
Anderson then served it out, ending things with a 128 mph service winner, and raised both arms overhead.
Now the 32-year-old South African moves on to a semifinal against Isner, the No. 9 seed who beat No. 13 Milos Raonic 6-7 (5), 7-6 (7), 6-4, 6-3 to reach his first Grand Slam semifinal in his 41st appearance.
Isner's 41 attempts to make a semifinal at a major is the second most in the 50-year professional era, behind Sam Querrey, who made the last four at Wimbledon last year with his 42nd try.
"Certainly the Grand Slam results haven't been there," said Isner. "But now I'm sort of rectifying that, I think."
Isner has yet to be broken at this year's tournament and saved the only break point he faced on Wednesday. Raonic hit 31 aces to Isner's 25 but was broken three times, including the last game of the match.
Nadal reached his first Wimbledon semifinal since 2011, winning a crowd-pleasing five-set duel against del Potro that took 4 hours, 48 minutes -- the longest match of this year's tournament -- and featured entertaining rallies between two of the biggest hitters in the game.
Del Potro finished with 77 winners to Nadal's 67 but failed to convert any of his five break points in the fifth set. Instead it was the Spaniard who earned the only break of the decider, and he closed out the win on his first match point -- leaving the fifth-seeded Argentine sprawled on the grass in exhaustion.
Awaiting Nadal in the semifinals is Djokovic, a three-time Wimbledon champion who reached his first Grand Slam semifinal since 2016 by beating No. 24 seed Kei Nishikori of Japan 6-3, 3-6, 6-2, 6-2.
Djokovic is a 12-time major champion who's been in something of a rut, due to right elbow troubles that lasted more than a year until he finally had surgery in February.
He's been flashing some anger this fortnight and did so again in the second set, bouncing his racket off the turf after failing to capitalize on three break points at 1-all. That earned a code violation from chair umpire Carlos Ramos.
When Nishikori let his own racket fly in the fourth set, he wasn't chastised, which prompted Djokovic to yell "double standards" toward Ramos -- drawing boos from fans.
"He claims that he didn't see what Nishikori has done, but apparently he always sees what I do," Djokovic said afterward, "something that I don't think is fair."
Later, Ramos warned Djokovic for a time violation, but that didn't seem to faze the Serb.
"I like the level of tennis that I'm playing on right now. I really do," said Djokovic, whose last major title came at the 2016 French Open. "I think with the performances I've had, I deserve to be in the semifinals. I don't want to stop here. I hope I can get a chance to fight for a trophy."
The Associated Press contributed to this report.