Novak Djokovic survived a gruelling fitness test under the brutal Melbourne sun on Thursday to stay alive at the Australian Open as Maria Sharapova laid down her title credentials.
With the temperatures touching an energy-sapping 40 Celsius (104 Fahrenheit) and ice-towels in use, the six-time champion came through a tough four-setter against Gael Monfils.
But it was not easy for a man who has barely played competitively for six months after an elbow injury.
He lost the first set before Monfils began badly wilting in the heat in the second and was heard at one point telling the umpire: "I'm tired and dizzy."
The Frenchman remarkably recovered to make a fight of it before a relieved Djokovic, seeded 14, came through 4-6, 6-3, 6-1, 6-3.
"It was tough conditions, brutal, especially the first 90 minutes," he said.
"I'm still not 100 percent, but building. I have a lot of faith and self-belief."
He now plays Spain's 21st seed Albert Ramos-Vinolas in the third round.
The furnace-like conditions took their toll on a host of players, including third seed and Wimbledon champion Garbine Muguruza who suffered with heat-blistered feet.
She was knocked out by 88-ranked Hsieh Su-wei from Taiwan 7-6 (7/1), 6-4 but refused to make excuses.
"I maybe could have done things better, but at the end, she deserves to win," she said.
Russian drawcard Sharapova was on Rod Laver Arena early and avoided the worst of the conditions as she showed why she should be again taken seriously in dismantling 14th seed Anastasija Sevastova 6-1, 7-6 (7/4).
It was the Latvian who ended her Grand Slam comeback in the last 16 of the US Open in 2017 as she returned from a drug ban. But not this time.
Sharapova, a five-time Grand Slam winner and the 2008 Australian champion, was unstoppable in racing through the first set before a battle in the second.
"You know, it was a warm day. I did my job in two sets against someone that's been troubling in the past for me," she said afterwards.
"I think I deserve to smile out there after that victory."
Being unseeded means she has her work cut out to reach another final.
Next up is in-form 2016 Australian Open champion Angelique Kerber, who beat Donna Vekic in two easy sets as she starts to rediscover her best again after a miserable last year.
Eighth seed Caroline Garcia also stayed in the title hunt, but she found it hard going against Czech teen Marketa Vondrousova who pushed her to three gruelling sets.
The Frenchwoman, who had a breakout year in 2017, winning two titles, eventually got over the line in almost two-and-a-half hours.
"My feet are burning," she said. "But we know it's like this in Australia – the next day it can be freezing."
Dangerous sixth seed Karolina Pliskova also progressed, dropping just two games against Beatriz Haddad Maia.
Among men through to the third round was fifth seed Dominic Thiem, who came from two sets down to beat American qualifier Denis Kudla.
Hungarian Marton Fucsovics piled more misery on the United States, dispatching 13th seed Sam Querrey with the American contingent – men and women – decimated in the early rounds.
Roger Federer rolls back into action later with the Swiss world No 2 headlining Rod Laver Arena in the evening against Jan-Lennard Struff.
The defending champion has made at least the third round each year since his debut at Melbourne Park in 2000. In contrast, Struff has failed to get further than the second round ever, at any Grand Slam.
In other matches, Alexander Zverev plays fellow German Peter Gojowczyk and 2014 Australian Open champion Stanislas Wawrinka continues his comeback from a lengthy injury lay off against Tennys Sandgren.
World No 1 Simona Halep, who was unconvincing in her first round encounter, takes on Canadian Eugenie Bouchard.
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