Daniil Medvedev struggled with the heat in Tokyo on Wednesday before reaching the Olympic quarter-finals, staying on course for a heavyweight clash with Novak Djokovic.
Second-seed Medvedev 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.
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 once more came into effect.
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, who will take responsibility?"
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.
World number one Djokovic continues his Olympic title bid against Spain's Alejandro Davidovich Fokina later Wednesday, with Japan's Kei Nishikori, the 2016 bronze medallist, taking on Ilya Ivashka of Belarus.
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.
Fourth-seed Svitolina will play Spain's Paula Badosa or Marketa Vondrousova, the conqueror of home favourite Naomi Osaka, for a place in the final in Tokyo.
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