Melbourne - World number one Simona Halep saved three match points to survive a titanic struggle and make the last 16 at the Australian Open on Saturday where she joined Karolina Pliskova and Caroline Garcia.
With the temperatures a manageable 26 Celsius at Melbourne Park after two days of oven-like conditions, the Romanian looked out for the count against American Lauren Davis.
But she finally got over the line 4-6, 6-4, 15-13 in a gruelling 3hr 44min on Rod Laver Arena to make the fourth round in a contest that took its toll.
"I'm almost dead," the tenacious Romanian said after the incredible battle, in which Davis lost a toenail and Halep served for the match four times.
"The feeling in my muscles is gone and I don't feel my ankle anymore," she added.
Davis is ranked just 76 in the world and was knocked out in the first round of all four Grand Slams last year, but you would never have known it.
Halep, a former quarter-finalist at Melbourne Park who slumped out in the first round last year, will next play Australian Ashleigh Barty or Japan's Naomi Osaka in her quest for a maiden Grand Slam title.
Sixth seed Pliskova also had a tough test, beating fellow Czech Lucie Safarova 7-6 (8/6), 7-5.
In contrast, US Open finalist Madison Keys was in fine touch as she benefits from the guidance of former great Lindsay Davenport.
Flying under the radar, the 17th seed has surrendered just 16 games on her way to the fourth round after beating Romania's Ana Bogdan 6-3, 6-4.
"Lindsay is amazing. We've had three years together and she has taught me how to handle big moments like this," said Keys, who made the Australian Open semis in 2015.
She will next test herself against French eighth seed Garcia, who was too strong for Belarussian Alaksandra Sasnovich, winning in three sets.
"I haven't done too well against her before and I want to improve," Garcia said of Keys.
Roger Federer and Novak Djokovic hold court later as they work to keep a potential Australian Open semi-final showdown on track.
The two greats of the game -- who have won 11 Australian Opens between them -- could meet in the last four if they maintain their winning ways, but both have tricky third-round tests ahead.
The Swiss defending champion headlines Rod Laver Arena in the evening, with the 19-time Grand Slam winner tackling France's Richard Gasquet.
On Margaret Court Arena, Serbia's Djokovic needs to find a way past 21st seeded Spaniard Albert Ramos-Vinolas.
Djokovic, who admits he is still not 100 percent as he returns from six months out with an elbow injury, struggled against Gael Monfils with his serve in hi slast match, sending down plenty of double faults.
In other third-round matches, Argentine 12th seed Juan Martin Del Potro plays tough Czech campaigner Tomas Berdych while fourth seed Alexander Zverev takes on South Korea's Chung Hyeon.
Maria Sharapova will be centre stage on Rod Laver Arena against Angelique Kerber in a fascinating encounter between the only two Australian Open winners left in the women's draw.
Both are 30, former world number ones and in good form.
"I look forward to these matches. I want to be playing against opponents that are former Grand Slam champions," said Sharapova, who is looking to rediscover her best on her way back from a 15-month drugs ban.
The victor will be rewarded with a clash against either Poland's Agnieszka Radwanska or Taiwan's Hsieh Su-wei.
Results from the Australian Open on Saturday:
Karolina Pliskova (CZE x6) bt Lucie Safarova (CZE x29) 7-6 (8/6), 7-5
Madison Keys (USA x17) bt Ana Bogdan (ROM) 6-3, 6-4
Simona Halep (ROM x1) bt Lauren Davis (USA) 4-6, 6-4, 15-13