Daniil Medvedev told the chair umpire "I can finish the match but I can die" as he struggled with the suffocating heat at Tokyo 2020.
A 6-2 3-6 6-2 win over Fabio Fognini on Wednesday was enough to see Medvedev through to the last eight at Ariake Tennis Park.
But the world number two struggled with 72 per cent humidity that meant an already hot 31 degrees Celsius felt like 37 degrees Celsius on the heat index.
An extreme heat rule meant Medvedev and Fognini were allowed to leave the court for 10 minutes at one stage of the contest.
Medvedev was in visible discomfort before serving, between points and at changeovers.
He had two medical timeouts before being asked by the chair umpire Carlos Ramos whether he could continue.
"I can finish the match but I can die," the Russian replied to Ramos, per ESPN. "If I die, are you going to be responsible?"
After the match, Medvedev – who along with Novak Djokovic has been vocally calling for matches to start later in the day to counteract the heat – described his struggles.
He said: "Even from the first set, I didn't feel good enough with my breathing. That's why I called the physio. I felt like my diaphragm had blocked.
"I couldn't breathe properly. I think it was the most humid day we have had so far.
"Then, on the second set, I just had darkness in my eyes, like between every point I didn't know what to do to feel better.
"I was bending over, and I couldn't get my breathing together. I was ready to just fall down on the court.
"I knew there was a 10-minute break. So I went under the cold, freezing shower.
"When you have such a change of temperature and go out on the hot court, you can fully cramp, and it finishes the match for you, either that or you feel better. I was lucky I felt better.
"I don't care too much [about closing the roof], to be honest because I don't know if they have AC [air-conditioning].
"It can be actually more humid and hot when they close it, but they should start the matches later. I said it in the first round, and I'll continue saying it.
"All the players I know said this is not normal to start at 11am [local time].
"[Djokovic] went to ITF and talked to them, and they gave him reasons - I heard maybe from tomorrow they're going to change it, but let's see."
Following the Medvedev match, organisers were quoted as saying they were "considering" making a change, starting from Thursday's action.
Paula Badosa also struggled on Wednesday and ultimately had to leave the court in a wheelchair after retiring with heatstroke from her quarter-final match against Marketa Vondrousova.
The Spaniard also withdrew from her mixed doubles match later alongside Pablo Carreno Busta, ending their hopes.
Carreno Busta is still in the singles and will face Medvedev next.
Vondrousova, who had won the first set before her opponent withdrew, said: "It was a big struggle from the beginning because I warmed up in the morning and I felt it was really hot and humid.
"Also, I was a bit tired from Monday because I had doubles too. But I knew [Badosa] had [played singles and doubles] too.
"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."