The pick of the day was Danish Caroline Wozniacki's win over 11th seed Kvitová of the Czech Republic.

The 33-year-old former world number one turned back the clock as she got the better of Kvitová 7-5, 7-6.

"Being out here on Arthur Ashe Stadium, night session, playing in front of a packed crowd, this couldn't be better," Wozniacki said.

"It's a dream come true.

"If you'd asked me three years ago, I would have said I'll never be back here playing on this court.

"But to be back and to beat the world No. 11 feels very, very special."

Meanwhile, Dominic Stricker of Switzerland, who is making his debut at the US Open, got the better of Greek star Tsitsipas in a five-set thriller.

The match that lasted more than four hours saw Tsitsipas serve for the match at 5-3 in the fourth set before a resilient Stricker beat him 7-5, 6-7, 6-7, 7-6, 6-3.

Zhu Lin of China also produced a shock win over two-time Olympic medallist and three-time US Open finalist Azarenka of Belarus, when she triumphed 6-3, 6-3 .

Her compatriot Zhang Zhizhen continued the Chinese dominance on the day as Norwegian Ruud, who was the runner-up last year, exited after a 4-6, 7-5, 2-6, 6-0, 2-6 loss.

Meanwhile, defending women's singles champion Iga Świątek of Poland had an easy 6-3, 6-4 win over Daria Saville.

Serbian 23-time Grand Slam champion Novak Djokovic is now on a seven-match winning run, and showed no signs of slowing down in his 6-4, 6-1, 6-1 victory against Bernabe Zapata Miralles of Spain.

Home favourites Coco Gauff and Frances Tiafoe were also among the winners today.

Gauff, who won titles in Washington and Cincinnati, before the US Open cruised to a 6-3, 6-2 win against Mirra Andreeva of Russia.

Her compatriot Tiafoe did not waste any time in dumping Austrian Sebastian Ofner out of the tournament, with a 6-3, 6-1, 6-4 victory.