What you need to know:
- The Russian second seed defeated Italy's Fabio Fognini 6-2, 3-6, 6-2 to set up a last-eight meeting with Pablo Carreno Busta of Spain at Ariake Tennis Park, staying on course to meet Novak Djokovic for the title.
- Two-time Grand Slam runner-up Medvedev, who had urged organisers to delay start times after his opening match, again found the temperatures testing as the extreme weather policy was implemented.
Daniil Medvedev struggled with the heat in Tokyo on Wednesday before battling through to the quarter-finals of the Olympics, even asking the chair umpire who would be responsible if he died.
The Russian second seed defeated Italy's Fabio Fognini 6-2, 3-6, 6-2 to set up a last-eight meeting with Pablo Carreno Busta of Spain at Ariake Tennis Park, staying on course to meet Novak Djokovic for the title.
Two-time Grand Slam runner-up Medvedev, who had urged organisers to delay start times after his opening match, again found the temperatures testing as the extreme weather policy was implemented.
"Even from the first set I didn't feel good enough with my breathing. I felt like my diaphragm was blocked, I couldn't breathe properly," said Medvedev, who took a medical timeout and received two visits from the trainer.
Asked by the umpire if he was OK during the second set, the Russian replied: "I can finish the match, but I can die. If I die, are you going to be responsible?"
"I think it was the most humid day we had so far, maybe the hottest," added Medvedev.
"The sun was pretty hot. At the end of the second set, I just had darkness in my eyes. I was bending over, and I couldn't get my breathing together. I was ready to just fall down on the court."
Following a 10-minute interval between the second and third sets, Medvedev broke Fognini and won the first three games of the decider.
He saved three break points at 4-2 before clinching victory after two hours and 25 minutes.
Tsitsipas sent packing
Medvedev renewed calls with the support of Djokovic to start matches later as temperatures peaked at 32 degrees Celsius (90 degrees Fahrenheit), with the heat index topping out at 37C.
"They should start the matches later, I said it from the first round, and I continue saying it," said Medvedev.
"I heard maybe from tomorrow they're going to change it, but let's see."
Stefanos Tsitsipas bowed out after the Greek third seed lost 2-6, 7-6 (7/4), 6-2 to Frenchman Ugo Humbert.
Tsitsipas required a medical timeout for an injury to his right leg at the end of the second set as Humbert booked a clash with Russia's Karen Khachanov.
World number one Djokovic continues his Olympic title bid against Spain's Alejandro Davidovich Fokina later Wednesday.
If he wins that he will face Japan's 2016 bronze medallist Kei Nishikori, who beat Ilya Ivashka of Belarus 7-6 (9/7), 6-0.
Ukraine's Elina Svitolina, the highest-ranked player left in the women's draw, reached the semi-finals with a 6-4, 6-4 win over Camila Giorgi of Italy.
"You know when you are higher ranked everyone wants to beat you and everyone is extremely motivated to beat you," said Svitolina.
"The Olympics is a very special event. In Ukraine, it's very big, even bigger than a Grand Slam.
"I'm really focused on any medal, try to be ready for anything that comes my way and try to be prepared for the conditions, for any opponents, and try to bring back the medal."
The fourth seed will play Marketa Vondrousova, the conqueror of home favourite Naomi Osaka, for a place in the final in Tokyo.
Spain's Paula Badosa retired due to heatstroke after losing the first set 6-3 to Vondrousova, leaving the court in a wheelchair.
Swiss ninth seed Belinda Bencic beat French Open runner-up Anastasia Pavlyuchenkova in three sets.