Simona Halep suffered a huge shock at the US Open at the hands of Taylor Townsend as Coco Gauff and Naomi Osaka booked a mouth-watering third-round clash in New York.

Halep had been considered one of the favourites for the women's singles title but saw a one-set lead snatched away by Townsend, who produced a thrilling comeback to claim the biggest win of her career on Thursday.

Townsend will face another Romanian, Sorana Cirstea, next but the match of the third round pits defending champion and world number one Osaka against 15-year-old Gauff, who once again delighted the Louis Armstrong Stadium crowd by winning a brutal battle with Timea Babos in two hours, 23 minutes.

She becomes the youngest woman to reach round three since 1996 will face a champion in fine form after Osaka made short work of Magda Linette as her defence continued at pace.

Osaka's hopes of retaining the crown have been boosted by Halep's exit, and sixth seed Petra Kvitova has also been removed as a potential obstacle after her loss to Andrea Petkovic.

HALEP SHORT ON INSPIRATION

Townsend came to the net over 100 times against Halep, an aggressive tactic that worked superbly in her stunning 2-6 6-3 7-6 (7-4) comeback.

Halep, though, felt a difference in inspiration levels was key. She told a media conference: "She was very inspired of every ball. She came a lot to the net and didn't miss much. It's unbelievable.

"I was not inspired at all today, but I fought. I thought when I came back that I will take it and I will win it. But sometimes it goes the other way."

Kvitova was also left to reflect on what might have been after her 6-4 6-4 defeat to Petkovic, while ninth seed Aryna Sabalenka was knocked out 6-3 7-6 (7-3) by Yulia Putintseva, who followed up her Wimbledon win over Osaka to knock out a top-10 seed for the second straight slam.

Seventh seed Kiki Bertens, however, is through after a 7-5 6-4 win over Anastasia Pavlyuchenkova. Belinda Bencic and Anastasija Sevastova were three-set winners over Alize Cornet and Iga Swiatek respectively and Johanna Konta thrashed Margarita Gasparyan 6-1 6-0.

HOME HOPES SPRING ETERNAL

Townsend's success was the headline act of a day defined by victories for young Americans on the women's side.

It was Gauff, though, who closed out the day's action and did so in typically engrossing fashion. The teenager again went the distance and willed her way to a 6-2 4-6 6-4 triumph, showcasing her incredible movement, repertoire of shots and composure to a raucous home crowd.

Sofia Kenin dished out a bagel in her 7-6 (7-4) 6-0 win over Laura Siegemund, while Kristie Ahn needed eight match points to complete her 6-2 6-3 defeat of Anna Kalinskaya.

Danielle Collins threatened an upset against two-time Flushing Meadows finalist Caroline Wozniacki, but eventually went down 4-6 6-3 6-4 as the 2018 Australian Open champion set up a match with another of the game's brightest talents, Bianca Andreescu, who beat Kirsten Flipkens 6-3 7-5.

"I kind of know what to expect if I play her. I know that she's an incredible fighter," Andreescu said of Wozniacki. "She runs every ball down, and I know that it's not going to be easy. I'm just going to go out there and play my game."

BENCIC ASKS QUESTIONS OF VEKIC

Donna Vekic had to wait for the reporters to be ready for her in the media room after her 7-5 6-3 victory over Kaia Kanepi, giving Bencic the chance to put her through her paces in an impromptu interview.

The Croatian has plenty of reasons to be cheerful after reaching the third round in New York for only the second time.

Joining her in round three is Karolina Muchova, who eliminated 29th seed Hsieh Su-Wei 6-1 4-6 7-6 (7-2) but will now have to recover quickly as she faces 23-time grand slam winner Serena Williams on Friday.

Maria Sakkari will have a similarly quick turnaround in facing second seed Ashleigh Barty after overcoming Peng Shuai 6-7 (5-7) 6-4 6-2.

Elsewhere in the draw, Wang Qiang overcame Alison van Uytvanck, Anett Kontaveit fought back against Ajla Tomljanovic and Elise Mertens, Petra Martic and Julia Goerges were also victorious.