Organisers acceded to player requests to change the tennis schedule after Spain’s Paula Badosa suffered heatstroke and left the court in a wheelchair.
Badosa needed treatment after losing the opening set of her singles quarter-final 6-3 to Naomi Osaka’s conqueror Marketa Vondrousova.
She later recovered but pulled out of her mixed doubles opener alongside Pablo Carreno Busta, with her coach Javier Marti saying: ‘The conditions today were so tough to play in.
Paula Badosa is pictured in action during her quarter-final against Marketa Vondrousova
After losing the first set 6-3 the Spaniard needed treatment following the intense heat
‘In her last two points, she was feeling very bad, she was serving very slow. After she asked to get treatment, she had no energy left and couldn’t continue as she was feeling dizzy.’
Men’s second seed Daniil Medvedev also struggled and was heard to say during his third-round match against Fabio Fognini: ‘If I die, who will take responsibility?’
A number of players have complained about being forced to play in the middle of the day in high heat and humidity, with Novak Djokovic arguing that matches should start later in the day.
A shocking simulation shows how athletes competing in the Tokyo Olympics risk heatstroke, dehydration and exhaustion because of the extreme temperatures at what is set to be the hottest games on record.
Covered by a towel and carried off in a wheelchair, Badosa made a recovery but was forced to retire from her singles clash in the women’s tennis singles competition
Running in 90°F (32°C) heat and 90 per cent humidity can raise their core temperature over the ‘tipping point’ of 102°F (39°C) where it becomes dangerous, experts say.
The International Tennis Federation, which organises the event, had kept matches beginning at 11am but from Thursday that will change to 3pm.
The ITF said in a statement: ‘In the interests of player health and welfare and following extensive consultation, the ITF has announced a change of schedule due to the increasing heat and humidity currently being experienced in Tokyo.
‘The decision to start matches at 3pm from Thursday is possible due to the outcomes of today’s matches across the five competitions being staged and the size of player field, and is designed to further safeguard player health.
‘It has been made following consultation with the IOC, Tokyo 2020, Olympic Broadcast Services as well as the Olympic Tennis Event players, referee, medical experts and other key stakeholders.’
Novak Djokovic has been among the leading players who have called for later start times
Medvedev lost the second set against Fognini but recovered to win 6-2 3-6 6-2 and reach the quarter-finals.
He said later: ‘Even from the first set, I didn’t feel good enough with my breathing. I felt like my diaphragm had blocked. I think it was the most humid day we have had so far.
‘Then, in the second set, I just had darkness in my eyes. 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.
‘It helped that I won the first set, so 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, or you feel better. I was lucky I felt better.’
Medvedev took exception to being asked about whether he felt a stigma of cheating following the ban on athletes competing for Russia, calling for the journalist who asked the question to be barred from the Olympics.
Daniil Medvedev has also voiced his concerns over the heat and humidity the players are being forced to play in, saying: ‘If I die, who will take responsibility?
Djokovic remains a red-hot favourite to win a first singles gold, and he eased to a 6-3 6-1 victory over Spain’s Alejandro Davidovich Fokina before returning to the court to win his mixed doubles opener alongside Nina Stojanovic.
The Serbian will next take on big Japanese hope Kei Nishikori, who has shown strong form in Tokyo and was a 7-6 (7) 6-0 winner over Ilya Ivashka.
There was a shock on Court Two where third seed Stefanos Tsitsipas was beaten 6-2 6-7 (4) 6-2 by France’s Ugo Humbert, but fourth seed Alexander Zverev continues to look strong, beating Georgian Nikoloz Basilashvili 6-4 7-6 (5).
Fourth seed Elina Svitolina has arguably underachieved at the grand slams but she is having a great run in Tokyo and guaranteed she will play for a medal for Ukraine by beating Camila Giorgi 6-4 6-4 to set up a clash with Czech Vondrousova.
Swiss ninth seed Belinda Bencic is also into the last four after a 6-0 3-6 6-3 victory over Russian Anastasia Pavlyuchenkova and will take on Kazakh Elena Rybakina, who knocked out the last remaining slam champion, Garbine Muguruza, 7-5 6-1.