Donna Vekic served the second set against Lulu Sun and double-faulted five times — the second-most in a match in Wimbledon history. It was an incredible implosion, or at least it would have been if we hadn’t seen this kind of struggle from Vekic before. She suffered a painful defeat from an advantageous position against Serbia’s Olga Danilovic at the French Open.

She was a set down at the fairytale Wimbledon, a qualifying event outside the world’s top 100. She had lost her previous two Grand Slam quarterfinals. It felt like a case of here we go again.

But then Vekic did something quite remarkable. She reset, broke Sun in the next game to take the second set, and promptly won the first 13 points of the deciding set to take a 3-0 lead. That put her more than halfway to the “golden set,” when you win one without losing a point. In the end, she had to settle for a 6-1 mauling, which worked well as an exclamation point in the first two sets, which finished 5-7, 6-4. It’s her first Grand Slam semifinal in 43 tries.

Much of the explanation for the turnaround is that Sun broke down physically, with nothing left in the tank after battling through qualifying and playing three three-setters in her four main-draw matches en route to the quarterfinals. But much of the credit also goes to Vekic, who said afterward that she channeled her anger at herself into something positive.

This was truly a momentous change in history.

The biggest change in Carlos Alcaraz, who was in the doldrums six months ago, may be happening in his brain.

Alcaraz has been quite open about his lulls in focus, especially when his game slips away. A few wayward forehands and the youngest world No. 1 in the history of the rankings would go into a spiral.

After beating Tommy Paul 5-7, 6-4, 6-2, 6-2 in the quarterfinals on Tuesday, Alcaraz spoke about how he has come to realise that playing badly doesn’t necessarily mean he has to lose.

“It’s going to be really hard to play my best tennis every match,” he said. In the first set against Paul, the American dominated in rallies of five to eight shots, winning 14 to Alcaraz’s seven. Alcaraz closed that gap in the next set, using his own dominance on shorter points to stay ahead.

“I know there will be matches where I can’t show my best tennis, even though I have to try to win them.

“I think that’s what the Big Three did during their career, they’re not going to play their best tennis. Even in that way, they’re going to find their good tennis to win those matches. That’s what I think.”

Time on tour helps, too. After more than three years of watching Alcaraz, his opponents know that the magic can strike again at any moment. One miraculous point, like the forehand down the line he hit against Ugo Humbert in the previous round, and he can start running downhill.

“Half the job when you’re out there is not to let him win one of those crazy points, because when he does, he’s going to get going,” Paul said. That’s a bit of a problem, because those crazy points only happen when he’s on his heels. Not letting Alcaraz get into trouble? If that’s the secret, his opponents are going to have to essentially reinvent the sport.

Discussing the conditions at Wimbledon this year, Vekic’s coach Pam Shriver said The Athletics on Tuesday that she had never seen so much humidity and dampness in the forty years she has lived here.

Her pupil Vekic can hit through the field and when you are as good a hitter as she is, the humidity can work to your advantage, something few of her rivals can do.

But physically it is tough for everyone to play in such a humid environment.

“The conditions were not easy today because when the roof is closed it is very humid,” Daniil Medvedev said after his five-set victory over Jannik Sinner.

“It’s very… not even humid, but you don’t have much air. So at a certain point in the match you feel like you lose your concentration because it’s just too much, like this humidity, the sound of the rain. You can’t hear the sound of your shots anymore. It’s like something is constantly falling on your head, so it’s not easy.”

It seemed that the humidity exacerbated the dizziness Sinner reported afterwards, forcing him off the court for nearly 10 minutes in the third set. He downplayed the significance of the conditions afterwards, but when he was on the court the humidity was noticeable and the conditions were clearly unforgiving.