No.2 seed Caroline Wozniacki is hoping to become the 13th player seeded in that position to win the US Open during the Open era. The last player to do so was Angelique Kerber in 2016.
Kerber tackles Johanna Larsson in the second round. She holds the second-highest rate on tour for advancing to at least the quarterfinals of a tournament in 2018, having done so in 10 of her 14 events (71%).
Petra Kvitova can equal WTA World No.1 Simona Halep for 2018 Tour victories if she overcomes Wang Yafan. She has picked up 45 wins to date, suffering 11 defeats in the process.
Although Monica Puig is ranked 49 places below No.6 seed Caroline Garcia on the WTA Ranking, the World No.55 holds a 3-0 head-to-head lead over the Frenchwoman. She has not reached the third round of a Grand Slam since Roland Garros in 2016, however.
Jelena Ostapenko is hoping to make it seven successive second-round victories at Grand Slams. She faces home favourite Taylor Townsend in the pair’s first career meeting.
WTA World No.11 Daria Kasatkina has enjoyed a hugely successful 2018 to date; she has earned half of her career prize money from this season alone ($2.3 million).
Madison Keys, the 2017 runner-up, is one of an elite group of four players who have reached at least the quarterfinals in two of the three Grand Slams to date this year.
Maria Sharapova has typically thrived under the floodlights on Arthur Ashe; she has won all of her previous 20 evening matches on the court.
Cloudy with spells of sunshine. Maximum temperature: 32C/90F.
Steve Tignor of tennis.com looks at how Sloane Stephens survived an uncomfortable test against Anhelina Kalinina.
Another Serena v Venus encounter is looming, and David Waldstein of the New York Times has profiled the rivalry.
Simona Halep struggled to explain her poor record at the US Open, suggesting the atmosphere around the city is part of the reason for her toils.
ORDER OF PLAY
Check out all of Day 4's scheduled women's matches on the WTA website here.