US Open 2018: Caroline Wozniacki & Petra Kvitova into second round
Australian Open champion Caroline Wozniacki beat Australian Sam Stosur 6-3 6-2 in hot conditions to reach the second round of the US Open.
Second seed Wozniacki, 28, broke the 2011 champion's serve five times on a day when temperatures in New York are expected to top 32C with high humidity.
The Dane plays Lesia Tsurenko next.
Organisers implemented the extreme heat policy at Flushing Meadows with a 10-minute break between the second and third sets in women's singles matches.
There will be a 10-minute break between the third and fourth sets of men's singles matches.
Wimbledon champion and fourth seed Angelique Kerber saw off Russian Margarita Gasparyan 7-6 (7-5) 6-3 and faces Swede Johanna Larsson in the second round.
Two-time Wimbledon champion Petra Kvitova is also into the second round after beating Belgian Yanina Wickmayer 6-1 6-4.
The Czech fifth seed, 28, broke serve twice to take the first set and won five successive games from 4-1 down in the second. She will play China's Yafan Wang next.
Two-time US Open runner-up Wozniacki said: "I'm just glad to have won this one. It's definitely difficult. It's very hot out here. I just tried to cool down between games."
American 24th seed Coco Vandeweghe, a semi-finalist at Flushing Meadows last year, was knocked out in the first round by Belgian Kirsten Flipkens, 6-3 7-6 (7-3).
Latvian 10th seed Jelena Ostapenko, the 2017 French Open champion, beat Germany's Andrea Petkovic 6-4 4-6 7-5 to set up a second-round meeting with American Taylor Townsend.
Japan's Naomi Osaka, seeded 20th, defeated German Laura Siegemund 6-3 6-2 and will play Israel's Julia Glushko.
Top seed Simona Halep was knocked out in the first round on Monday.