Paula Badosa was forced to withdraw from her quarter-final against Marketa Vondrousova and taken from the court on a wheelchair after suffering from heatstroke at Tokyo 2020.
Tuesday saw heavy downpours in the Japanese capital, but the hot and humid conditions from earlier in the week returned early on Wednesday with temperatures at times going above 30 degrees Celsius.
Vondrousova, who had shocked home favourite Naomi Osaka in the previous round, won the first set 6-3 at Ariake Tennis Park but her opponent was clearly struggling as she prepared to play the second set.
She required medical assistance to depart the court, as Vondrousova progressed to the final four.
VONDROUSOVA COMMENTS ON THE HEAT
The conditions for the tennis in Tokyo have been a quite literal hot topic with both Daniil Medvedev and Novak Djokovic stating matches should start at 3pm so the majority can be played as temperatures cool.
Vondrousova explained how it was playing in the searing heat, saying: "It was a big struggle from the beginning.
"I warmed up in the morning and I felt it was really hot and humid. Also, I was a bit tired from yesterday because I had doubles too.
"But I knew she had too [singles and doubles]. I felt like we both were struggling from the beginning.
"I was just thinking, you have to stay there mentally, just fight for every point and just see what happens. It's good for me that I can have some rest now.
"It's all about the head too. You have to stay there mentally and fight. Even when you lose the point, you have to get up and fight again. It's really a struggle here with the weather, but that's it, we have to fight."
OLYMPICS LIKE A SLAM FOR SVITOLINA
Next up for Vondrousova is a last-four meeting with Elina Svitolina, the fourth seed and highest-ranked player left in the women's draw.
The Ukrainian was a 6-4 6-4 victor over Camila Giorgi and talked up the significance of winning Olympic gold.
"I know that for Ukraine, [the Olympics] is a really big thing," Svitolina said.
"I value the Olympics as a grand slam, and I tried to prepare to bring my best tennis. Here I am in the semi-final, and I can get a chance to get a medal. It's very special for me, but I try to take one match at a time."
Belinda Bencic (9) came through 6-0 3-6 6-3 against Anastasia Pavlyuchenkova on the other side of the draw. She will face Elena Rybakina (15), who was too good for seventh seed Garbine Muguruza in a 7-5 6-1 win.
Ash Barty was beaten along with partner Storm Sanders in the women's doubles quarter-finals earlier on Wednesday but the world number one bounced back to win her first-round mixed doubles match with partner John Peers.
The Australian duo beat Argentina's Horacio Zeballos and Nadia Podoroska 6-1 7-6 (7-3).