Maria Sharapova has called for tennis officials to clear confusion over what qualifies as unplayable conditions after she was forced to play in temperatures above 40 degrees at the Australian Open.
The heat forced matches to be suspended at 1.52pm on Thursday after tournament referee Wayne McEwen used his discretionary powers to stop play after the wet-bulb temperature reached a certain level and was forecast to remain there for at least an hour.
Under policy guidelines matches are suspended at the end of the set in progress when the policy was invoked, leaving Sharapova in a fight to the death in the third set against Italian Karin Knapp.
Temperatures reached a high of 42.4 degrees during the match on Rod Laver Arena, and later peaked at 43.3 degrees at Melbourne Park.
Despite the policy being applied, Sharapova and Knapp were forced to continued for 50 minutes before the Russian claimed a 6-3, 4-6, 10-8 victory in three hours, 28 minutes.
The third set lasted 114 minutes, the longest match Sharapova has played in 42 grand slam appearances. She later called for players to be better informed.
''There is no way of getting around the fact that the conditions were extremely difficult, and have been for the last few days,'' she said.
''It's a tough call. I think the question I have is no one really knows what the limit is. Not the players or the trainers themselves when you ask them when will the roof be closed. No one actually knows what that number is in comparison to humidity or the actual heat.
''It just depends on, I'm not sure who, a referee or the meteorologist, and there are just a lot of questions in the air that maybe should be solved … I asked the trainer the other day, 'What does it take for the roof to be closed or matches to be stopped?' She said, 'We have no control over this.'''
It was the first time the extreme heat policy has been applied since 2009, when the tournament was suspended on consecutive days due to temperatures as high as 45 degrees.
The hottest temperature recorded at the Open, 45.5 degrees, was on January 29 that same year.
All matches on the outside courts on Thursday were suspended at the end of the set in progress until 6pm. Late matches were postponed until Friday.
Jo Wilfried-Tsonga's match against Thomaz Bellucci on Hisense Arena was suspended to let the roof close at the end of the second set. The roof was also closed on Rod Laver Arena after Sharapova's match for the start of Caroline Wozniacki's battle against Christina McHale, which the Dane claimed with a 6-0, 1-6, 6-2 victory.
But Sharapova insists she had no idea the extreme heat policy had been applied until after the match.
''I didn't even know there was no play when I left the court. But it seems a little strange that the WTA Tour trainers don't know what that threshold is.''
Fifth seed Agnieszka Radwanska, who played under the roof on Hisense Arena, said the heat was ''ridiculous'' even indoors, and conditions had been a talking point among players.
The extreme heat policy is applied when the wet bulb globe temperature exceeds 30.1 degrees, allowing the tournament referee to suspend play at his discretion.
Given the extreme heat in Melbourne, women in the singles draw were already allowed a 10-minute break between the second and third sets and ice vests are provided on all courts.
Attendance at the Open was 33,419, down just a few thousand from the same day last year.
with Emma Quayle