No.13 seed Belinda Bencic ended No.1 seed Naomi Osaka's only previous title defence - also in a fourth-round encounter - in Indian Wells this March, winning 6-3, 6-1 for the first of two victories over the Japanese player this year, triumphing 3-6, 6-2, 7-5 in the Madrid quarterfinals as well. Those results take Bencic's head-to-head lead to 2-1: the pair first played in the first round of an ITF W25 event in Pelham in 2013, when a 15-year-old Osaka - ranked World No.1028 - defeated a 16-year-old Bencic 6-3, 6-3 two months before the Swiss player became junior World No.1.
With the losses of Ashleigh Barty and Karolina Pliskova yesterday, World No.1 Naomi Osaka now controls her destiny: if she defends her title, she will remain in the top spot; if she does not, Barty will return to No.1.
One month ago, Kristie Ahn defeated Elise Mertens 6-3, 6-3 in San Jose for a milestone win - the American's first Top 20 scalp, and one that both put her into her maiden Premier quarterfinal and sealed her victory in the USTA's US Open Wildcard Race - and today, the wildcard has a chance to reprise it. Overall, Ahn and Mertens are level at 2-2, with their other three encounters taking place in 2016 - including a previous meeting in the final round of US Open qualifying that year, which the Belgian won 6-1, 6-4 to make her Grand Slam main draw debut.
Kristie Ahn is the first Asian-American in the second week of a Slam since Lilia Osterloh reached the fourth round of the 2000 US Open, and she is bidding to become the first to reach the quarterfinals since Kimberly Po at the 1997 Australian Open.
No.26 seed Julia Goerges leads the head-to-head against No.23 seed Donna Vekic 3-0, although this will be the first time the pair of played on outdoor hard courts. Goerges' first two victories, in the second round of Budapest 2017 and the fourth round of Wimbledon last year, were both in straight sets - but in the Luxembourg quarterfinals last October, Vekic won her first set of the series before falling 6-3, 3-6, 6-3. Vekic is bidding to become the second ever Croatian US Open quarterfinalist following Ana Konjuh in 2016.
Belinda Bencic has posted five Top 5 victories and eight Top 10 wins in 2019 - more than anyone else on Tour in either category. The Dubai champion also holds three wins over reigning World No.1s - in addition to her pair of Osaka wins this year, Bencic also defeated Serena Williams 3-6, 7-5, 6-4 in the 2015 Toronto semifinals en route to the title.
Taylor Townsend is bidding to become the third qualifier to reach the US Open quarterfinals in the Open Era, joining Barbara Gerken in 1981 and Kaia Kanepi in 2017. Kristie Ahn is aiming to become the first wildcard to make the last eight since Kim Clijsters' title run in 2009, and Bianca Andreescu is seeking to be the first player to make the quarterfinals on her US Open debut since Belinda Bencic in 2014. A win today would also make Andreescu the third Canadian quarterfinalist at Flushing Meadows following 1984 semifinalist Carling Basset-Seguso and 1992 quarterfinalist Patricia Hy-Boulais.
ORDER OF PLAY
For full order of play, visit usopen.org.
Players such as Ashleigh Barty, Marketa Vondrousova and Bianca Andreescu have all made the case for variety as the future of tennis this year - but baseline power is hitting back at the US Open, writes Steve Tignor for tennis.com.
From opposition analysis to pre-tournament preparation, find out what a day in the life of Ashleigh Barty's coach Craig Tyzzer looks like in a Q&A with TenniSmash.
Doubles World No.1 Barbora Strycova has had the best summer of her career at the age of 33 - and discussed fashion, standing up for herself and the pressures of being a junior prodigy in an exclusive interview with David Kane for wtatennis.com.