Novak Djokovic and Coco Gauff through as players feel the heat at US Open
Sweat-soaked 24-time Grand Slam champion Djokovic looked far from comfortable under the lights at Arthur Ashe Stadium and had to battle from 2-4 in the second set before seeing off fellow Serb Laslo Djere, who retired injured at 6-4, 6-4, 2-0.
"It's not what we want. It's not what the crowd wants, to see a walkover," Djokovic said.
"But he obviously had an injury that took him out of the tour for some time and he is struggling to come back physically to this level. He's such a good player, especially in these conditions. It should have been his second set.
"Overall, it was a big fight. Over two hours for two sets. I served awful. Playing without the serve, you have to grind, you have to run. So I guess I had to rely on my baseline game."
German fourth seed Alexander Zverev wasted little time in blazing conditions earlier in the day as he dispatched Frenchman Alexandre Muller 6-4, 7-6(5), 6-1 on Louis Armstrong Stadium.
"I'm happy to be through in three sets because I think the weather and conditions were obviously very difficult today. Very hot, very humid," Zverev said.
"The less time I spend on the court, the better it is."
American Madison Keys was equally relieved to cruise past Australian qualifier Maya Joint 6-4, 6-0 at Arthur Ashe Stadium.
"I just wanted to get on and get off," 2017 runner-up Keys said after her 62-minute victory.
Tomas Martin Etcheverry vomited on court amid the stifling conditions during a five-set win over Francisco Cerundolo, while players on the other courts wrapped themselves in ice towels and guzzled energy drinks during changeovers.
Barely troubled
Last year's finalist Sabalenka is no stranger to hot and humid conditions as a resident of Miami and the big-hitting Belarusian was barely troubled during her 6-3, 6-1 win over Italian Lucia Bronzetti.
She celebrated the win by taking pictures with a young fan outfitted in similar gear to the second seed and sporting a temporary tiger tattoo to match that on Sabalenka's left forearm.
"I looked up and I saw on the big screen, like, mini-me. It was so cute," Sabalenka said.
"It's such a motivation to keep going, to inspire the young generation. That's the main goal. That was an adorable moment."
Gauff was also in roaring form as the American overcame early mistakes to defeat unseeded German Tatjana Maria 6-4, 6-0 while three-time runner-up Victoria Azarenka battled through a migraine to beat Clara Burel 6-1, 6-4.
Zheng Qinwen of China was given an early headache by Russian 20-year-old Erika Andreeva before the Olympic champion prevailed 6-7(3), 6-1, 6-2 after a 10-minute heat break midway.
Sixth seed Andrey Rublev dropped the first two sets against Arthur Rinderknech but dug deep to secure a 4-6, 5-7, 6-1, 6-2, 6-2 victory, while eighth seed Casper Ruud was dragged into a fight by another tenacious Frenchman in Gael Monfils.
That evening match on Grandstand was suspended midway due to a lightning warning with supporters asked to leave for their own safety before Ruud later completed a 6-4, 6-2, 2-6, 7-6(3) win.
Taylor Fritz kept the flag flying for the American men as he eased past Matteo Berrettini 6-3, 7-6(1), 6-1 after Frances Tiafoe advanced when an ailing Alexander Shevchenko retired and Ben Shelton beat Roberto Bautista Agut 6-3, 6-4, 6-4.