Madison Keys has reached the fourth round for the third straight year at the US Open, but never progressed beyond this stage here - overall, she is 2-5 in Slam rounds of 16. Her opponent today, Elina Svitolina, has now reached the second week at three Slams out of four with her run this year - but she has only reached the quarterfinals at Roland Garros.
Either Svitolina or Keys will score a career-best US Open victory today. Each has only one Top 50 win under her belt in Flushing Meadows so far: Svitolina's first-round defeat of No.21 Dominika Cibulkova in 2013 and Keys' third-round defeat of No.15 Agnieszka Radwanska in 2015.
Lucie Safarova leads her head-to-head against CoCo Vandeweghe 3-1, including two wins on US hard courts and a 4-6, 6-4, 6-1 victory in the second round of Indian Wells this year. The American's only win was their first meeting, in the fourth round of Wimbledon in 2015, 7-6(1), 7-6(4).
This year's US Open marks the third consecutive Slam at which one or more players entered on a special ranking have made the second week. At Roland Garros, Petra Martic reached the fourth round out of qualifying; at Wimbledon, Martic repeated the feat, and was joined by Magdalena Rybarikova and Victoria Azarenka; and in Flushing Meadows, Kaia Kanepi (whose frozen ranking got her into qualifying) and Sloane Stephens have accomplished it.
Jennifer Brady has reached the second week at two majors in 2017, having made the fourth round as a qualifier at the Australian Open on her Slam debut. However, she has failed to win a WTA main draw match at any tournament outside the Slams. Her overall career record at Slams is 7-3, while at other WTA events it is 2-11.
CoCo Vandeweghe is the sole former US Open junior champion left in the draw. Her girls' title run in 2008 included a semifinal win over Kristina Mladenovic before beating Gabriela Paz in the final.
20-year-old Daria Kasatkina, the youngest player remaining, last faced Kaia Kanepi in the very different setting of the quarterfinals of the ITF $50,000 tournament in Saint-Malo in 2015. It was a week after Kasatkina had reached the US Open third round on her Slam debut, and she triumphed in that match 2-6, 6-1, 6-1 - going on to win the event, a result that saw the Russian break the Top 100.
The five American women in the fourth round mark the largest US cohort in the second week in New York since 2002. Two of those home players, Venus Williams and Sloane Stephens, reached the quarterfinals yesterday, with Madison Keys, CoCo Vandeweghe and Jennifer Brady all in action today. The last time the USA had five quarterfinalists in a major was also the 2002 US Open: Serena and Venus Williams, Monica Seles, Lindsay Davenport and Jennifer Capriati.
Four unseeded players - Daria Kasatkina, Kaia Kanepi, Lucie Safarova and Jennifer Brady - are in fourth-round action today, of seven in total who had reached this stage. This is the highest total at the US Open since 1997, back when only 16 players were seeded. That year, the unseeded players in the second week were Florencia Labat, Rachel McQuillan, Magui Serna, Venus Williams, Joannette Kruger, Karina Habsudova and Sandrine Testud.
Kaia Kanepi has a strong 5-1 record in Slam fourth rounds. Her only defeat at this stage came at the 2014 US Open to Serena Williams. Ranked No.418, she is seeking to become the lowest-ranked US Open quarterfinalist since unranked Kim Clijsters in 2009.
Elina Svitolina is bidding to become the first Ukrainian quarterfinalist in New York since Kateryna Bondarenko in 2009.
Kaia Kanepi's return to high-level tennis after two years suffering from the effects of the Epstein-Barr virus and plantar fasciitis in both feet has been one of the stories of the tournament. In her time away, she took up ice-road driving in Finland - find out more with Dave James for Yahoo! Sports.
During her two years at UCLA, Jennifer Brady was a college standout, Helene Elliott reports for the LA Times.
The eight-woman battle for No.1 at the start of the tournament is now between three players, and in the hands of just two. WTA Insider breaks down the scenarios.
Relive last night's brilliant performances by Petra Kvitova and Anastasija Sevastova that saw them book US Open quarterfinal berths.