• Earlier, top seed Iga Swiatek and sixth seed Coco Gauff underlined their credentials with comfortable wins.
Caroline Wozniacki claimed the biggest win of her fledgling comeback by beating 11th seed Petra Kvitova to reach the US Open third round.
Former world number one Wozniacki, who retired in 2020 and has since had two children, won 7-5 7-6 (7-5) in Wednesday’s night session in New York.
“It is a dream come true,” said the 33-year-old Dane.
Earlier, top seed Iga Swiatek and sixth seed Coco Gauff underlined their credentials with comfortable wins.
Defending champion Swiatek beat Australian Daria Saville 6-3 6-4, while 19-year-old American Gauff won 6-3 6-2 against Russian teenager Mirra Andreeva.
Wozniacki joined them in the third round after an impressive performance against long-time rival Kvitova, also 33, in only her third tournament back.
After Czech Kvitova saved two match points when serving at 5-4, Wozniacki showed her trademark grit to take a fourth opportunity in the tie-break. After sealing victory, she became emotional in her chair as the crowd on Arthur Ashe Stadium showed their appreciation.
“Being out here on Ashe in a night session couldn’t be any better and to beat the world number 11 is so special,” said two-time finalist Wozniacki, who won her sole major title at the 2018 Australian Open.
“Three years ago if you’d asked me, I didn’t think I was ever going to play on one of those courts again in the US Open. It just feels pretty incredible to be out there and winning a match like that.”
The victories for Swiatek and Gauff keep the pair on course to potentially meet in the quarter-finals. Poland’s Swiatek is looking to become the first woman to defend her US Open title since American Serena Williams won a hat-trick of titles from 2012.
The world number one will play Slovenia’s Kaja Juvan on Friday for a place in the last 16.
“It wasn’t easy but I’m happy I tried to play my game and play aggressively with a lot of intensity and I’m just happy to be in the third round,” Swiatek said.
Gauff, looking for her first major singles title, had to fight back to see off German qualifier Laura Siegemund in the first round, but produced an impressive display in her second-round match to progress.
Andreeva, 16, has enjoyed an incredible rise in recent months, reaching the last 16 of the Australian Open and Wimbledon to help her climb from 293 in the world in December to 62nd.