Rafael Nadal will face heat and his stiffest challenge so far at the Australian Open on Friday, while Caroline Wozniacki will be looking to prove a point in her third round match.
The Spanish world number one has so far been dominant in his search for a 17th Grand Slam title.
But it will be a tougher ask on Margaret Court Arena against Damir Dzumhur, the first seed he has faced in his comeback from a knee problem.
And with temperatures forecast to reach 42 Celsius (107.6 Fahrenheit), he is guaranteed a thorough workout against the 28th seed, although his evening slot will shield him from the worst.
"The only thing that I hope is if it is extreme conditions, the organisers shut the roof. That's all. I think it's a health issue," he said.
Extreme heat hit the tournament on Thursday, with some players struggling to cope.
Frenchman Gael Monfils said he was "dying" on court, while Novak Djokovic called the conditions "brutal".
Organisers can activate the extreme heat policy and halt play when the temperature exceeds 40 Celsius and the wet bulb globe temperature index hits 32.5 Celsius.
Despite being second seed, Denmark's Wozniacki has not impressed, needing to save two match points and rally from 5-1 down in an epic third set against little-known Jana Fett in round two.
She is the late match on Rod Laver Arena against Dutch 30th seed Kiki Bertens and will be looking to reassert herself.
Fourth seed Elina Svitolina also needed three sets in her last match, and with a round of 16 place at stake will have to pick up her game against 15-year-old sensation Marta Kostyuk.
The teen is the youngest Australian Open third round contestant since "Swiss Miss" Martina Hingis in 1996, and is full of confidence.
"You know, she has nothing to lose, she goes just for everything," admitted Svitolina.
Men's third seed Grigor Dimitrov also has plenty to prove after a huge second-round fright from a qualifier, who pushed him to five sets.
The Bulgarian world number three faces Russian rising star Andrey Rublev in an afternoon match that will be played in the hottest period of the day.
An intriguing night match on Rod Laver Arena pits Australian Nick Kyrgios against French veteran Jo-Wilfried Tsonga.
Tempestuous Kyrgios has been in fine form and will play either Dimitrov or Rublev for a place in the quarter-finals if he survives.
Sixth seed Marin Cilic is also in action, while 38-year-old Ivo Karlovic will be looking to keep his vintage run going.
© 2018 AFP