Tennis fans could be in for a late night after Melbourne's heatwave led to the suspension of Australian Open matches, creating a scheduling backlog.
The mercury at Melbourne Park peaked at 38.5C at 5.30pm local time and was still hovering in the mid 30s past 8pm.
The sweltering heat scared spectators away, with a streak of attendance records broken after 51,048 came through the gates for the day session.
Play was officially halted on non-roofed courts shortly before 3pm because it was determined conditions had reached level five on the Open's heat stress scale.
Women's 13th seed Linda Noskova was locked at 2-2 with Xinyu Wang on Kia Arena when play was suspended.
Their clash did not resume resume until 7.30pm, with Xinyu winning through to the fourth round 7-5 6-4.
The hours-long delay pushed back the later match between men's 16th seed Jakub Mensik and American Ethan Quinn.
Doubles and junior singles matches were also suspended.
Play stopped to close the roof at the major courts, including Rod Laver Arena, where two-time defending champion Jannik Sinner battled serious cramp to beat American world No.85 Eliot Spizzirri 4-6 6-3 6-4 6-4.
"It was hot today," the Italian world No.1 said.
"Started to cramp a little bit in the third set, which then after time it went slowly away."
In 2019, the tournament implemented an extreme heat protocol using a "heat stress" scale, which factors in air temperature, radiant heat, humidity and wind speed to generate a reading between one and five.
If the scale hits five, play is suspended on outdoor courts, while the roofs are closed on Rod Laver, John Cain and Margaret Court arenas.
A 10-minute cooling break is allowed between the second and third sets for women's matches, and between the third and fourth sets for men's singles.
Play started at 10.30am, rather than 11.30am, to try to beat the heat, though the roof was open at both Rod Laver Arena and Margaret Court Arena to start the day.
Women's defending champion Madison Keys and world No.6 Jessica Pegula were first up and ripped through straight-sets victories in barely an hour to beat the heat.
World No.4 Amanda Anisimova said she took ice baths before and after the match to help her deal with the "really tough" conditions.
All three top Americans are based in Florida, and felt the combination of that grounding and their early starts helped them handle the heat.
"It started to get a little hot," Pegula said.
"I just tried to use the ice towels as much as I could, just pre-cooling a lot.
"Not necessarily that it felt that hot at the moment, but if it did start to creep up or if something happened and we go into a third, I definitely think it could kind of zap you pretty quick with how hot it could get.
"The fact that we haven't been playing that much in the hot temperatures I think is what gets people.
"You have no kind of tolerance to it, and then it all of a sudden comes out of nowhere. We're used to it happening here, but it's hard to prepare for that."
