Defending champion Naomi Osaka faces 15-year-old wildcard Coco Gauff in a blockbuster third round. Gauff is aiming to become the youngest player to reach the second week of the US Open since a 15-year-old Anna Kournikova reached the fourth round on her 1996 debut, and the youngest player to defeat a World No.1 since a 15-year-old Jennifer Capriati beat Monica Seles in the 1991 San Diego final. Osaka's Tour record against players younger than her is 6-3 overall and 4-1 in 2019, with her sole loss this year coming via retirement to Sofia Kenin in the Cincinnati quarterfinals.

Indian Wells and Toronto champion Bianca Andreescu has risen from World No.152 at the start of the year to her current World No.15 thanks to a phenomenal 40-4 win-loss record - and the big win that kicked it all off in the first week of 2019 was her 6-4, 6-4 defeat of Caroline Wozniacki in the second round of Auckland en route to the Canadian teenager's first WTA final. It was also the first of nine Top 20 wins so far this year for Andreescu - while a win for Wozniacki today in their first meeting since then would be her first Top 20 victory of the season. A first appearance in a major second week is also at stake for Andreescu, while for Wozniacki, a win would mean her first run to a Grand Slam fourth round since Roland Garros last year.

Former Roland Garros champion Jelena Ostapenko and wildcard Kristie Ahn have a rematch of one of the most dramatic matches of the season today - their first-round tilt in Bogota, which Ahn took 2-6, 7-6(5), 7-5, saving two match points, for her first career Top 30 win. Ostapenko had lost in the first round of all three majors this year before the US Open, where she has made the third round for the third consecutive year and will be bidding to reach the second week for the first time.

Gallery: 2019's winners from match point down

No.13 seed Belinda Bencic and No.21 seed Anett Kontaveit have never met in the pros - but Bencic did win their only junior meeting 6-4, 4-6, 6-2 en route to winning the 2013 Wimbledon girls' title, part of a 39-match winning streak in the Swiss player's final year in juniors. Bencic has reached but lost in the third round of every major this year so far; overall, her record at this stage is 4-6. Both Bencic and Kontaveit made the second week on their US Open debuts, with Bencic reaching the 2014 quarterfinals and Kontaveit the fourth round in 2015 - and both are seeking to return their for the first time since.

Belinda Bencic defeated Angelique Kerber and Jelena Jankovic to reach the US Open quarterfinals as a 17-year-old on her debut in 2014 (Getty)

No.7 seed Kiki Bertens faces No.26 seed Julia Goerges on hard courts for the first time today. Bertens leads the head-to-head 2-1, winning both of their clay encounters in the 2016 Nurnberg semifinals and the 2018 Charleston final, but Goerges got on the board on grass in their most recent meeting in the 2018 Wimbledon quarterfinals to win 3-6, 7-5, 6-1. Bertens is bidding to make the second week of a hard-court major for the first time in her career.

In juniors, Yulia Putintseva was undefeated against Donna Vekic, winning 2-6, 6-2, 6-3 at Wimbledon 2011 and 6-0, 6-2 at the US Open in the same year. However, Vekic has yet to drop a set in three pro meetings against Putintseva, winning their first-round tilts at Miami 2013 on hard courts, Madrid 2017 on clay and Eastbourne 2018 on grass. While Putintseva is a two-time Roland Garros quarterfinalist (2016, 2018) and Vekic has made the last 16 of Wimbledon 2018 and Roland Garros 2019, the winner today will make her debut in the second week of the US Open.

Taylor Townsend's progress means that there has been at least one qualifier in the US Open third round every year since 2007 except 2017. Of the 19 qualifiers who have previously reached this stage in that period, six have gone on to the fourth round: Anna-Lena Groenefeld in 2008, Camila Giorgi in 2013, Aleksandra Krunic and Mirjana Lucic-Baroni in 2014, and Johanna Konta and Anett Kontaveit in 2015. The American has reached this stage for the first time since her Grand Slam debut at Roland Garros 2014. Her opponent, Sorana Cirstea, is bidding to reach the second week of a major for the third time in her career following her 2009 Roland Garros quarterfinal and 2017 Australian Open fourth-round run.

No.25 seed Elise Mertens is the only player yet to drop serve in the tournament. The Belgian, who won her only prior meeting with Andrea Petkovic 6-2, 6-2 in the first round of Mallorca in June, has a second-week showing at each major under her belt - but a win would mean the first time she has reached that stage twice at any of them. 2011 quarterfinalist Petkovic, meanwhile, is bidding to make her first second-week run at a major since reaching the 2014 Roland Garros semifinals.


For full order of play, visit usopen.org.


When Taylor Townsend double faulted on her first match point against Simona Halep on Thursday, the American could have been forgiven for a flashback to Wimbledon, where she also squandered a match point before losing to Kiki Bertens - but she regrouped to write a new narrative, writes Matt Zemek for Tennis With An Accent

Ahead of their popcorn match today, Naomi Osaka and Coco Gauff - whose families have known each other for many years - have been forming a mutual admiration society, writes WTA Insider Courtney Nguyen.