MELBOURNE: Fourth seed Elina Svitolina ended the Australian Open hopes of young teenage pretender Marta Kostyuk on another searing hot day Friday, as organisers defended the tournament heat policy.
Marta Kostyuk, at just 15, was the youngest Melbourne Park third round contestant since "Swiss Miss" Martina Hingis in 1996, and was hailed after her previous win as "the future of tennis".
But she still has a lot to learn with fellow Ukrainian Svitolina handing out a 6-2, 6-2 lesson.
"She´s definitely got a bright future," said Svitolina, adding: "It´s very special for me to get past the third round."
Svitolina will next play another qualifier -- big-serving Czech Denisa Allertova who romped past Magda Linette 6-1, 6-4 -- for a place in the quarter-finals on Sunday.
In a tournament shorn of seeds, 81st ranked Petra Martic also swept into the round of 16, celebrating her 27th birthday by holding off a gritty challenge from Thai qualifier Luksika Kumkhum.
The Croat battled a succession of powerful winners from her opponent to prevail 6-3, 3-6, 7-5.
Her reward is a match against Belgium´s Elise Mertens, who beat struggling Alize Cornet of France in two tough sets.
Cornet was among players wilting in the 40 Celsius (104 Fahrenheit) heat, with a doctor taking her blood pressure early in the second set as she succumbed to the baking weather.
No matches have been called off so far at the opening Grand Slam of the year despite the soaring temperatures, with tournament organiser Craig Tiley defending the decision.
"The policy is from consultation with the players," he said. "These are professional athletes.
"We are at the end of the day an outdoor event. We want it to stay an outdoor event as long as possible but at the same time ensuring that the health and wellbeing of players is taken care of."
Organisers will only active the extreme heat policy and halt play or close roofs when the temperature exceeds 40 Celsius and the wet bulb globe temperature index hits 32.5 Celsius.
On Thursday, Novak Djokovic described the conditions as "brutal", complaining it was hard to breathe and they were "right on the limit".
Kyle Edmund was the first man to reach the round of 16, overcoming the elements in a fighting five-set win over Nikoloz Basilashvili.
The 49th-ranked Briton fought back to take the last two sets and win 7-6 (7/0), 3-6, 4-6, 6-0, 7-5.
He is the only British man in the main draw after Andy Murray´s injury withdrawal and will play either Croatia´s 38-year-old Ivo Karlovic or Italian Andreas Seppi in the fourth round.
Rafael Nadal will face his stiffest challenge so far in a night match on Margaret Court Arena when he takes on Damir Dzumhur, the first seed he has played in his comeback from a knee problem.
The Spanish world number one has so far been dominant in his search for a 17th Grand Slam title, but it is expected to be a tougher task against a player ranked 25.
Despite being second seed, Denmark´s Caroline Wozniacki has not impressed so far, 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.
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 takes on Russian rising star Andrey Rublev.
An intriguing night match pits Australian Nick Kyrgios against French veteran Jo-Wilfried Tsonga.