No.1 seed Elina Svitolina owns a 4-0 head-to-head lead against former World No.10 Daria Kasatkina. The Ukrainian has previously won 6-4, 5-7, 6-0 in the first round of New Haven in 2016; 7-6(4), 6-4 in the second round of Toronto in 2017; 6-4, 6-0 in the 2018 Dubai final; and 0-6, 6-3, 6-2 in the third round of Rome in 2018.
No.2 seed Aryna Sabalenka has met former World No.9 CoCo Vandeweghe once before - in the 2017 Fed Cup final in Minsk, with Vandeweghe winning 7-6(5), 6-1 en route to squeezing out a thrilling 3-2 win for the USA over Belarus. Now ranked World No.636 after a hiatus to recover from a foot injury, Vandeweghe's first-round win over Marie Bouzkova was the American's first singles match since Beijing last year and her first victory since beating Alison Riske in the 2018 's-Hertogenbosch quarterfinals.
Last year's runner-up Maria Sakkari faces qualifier Mayo Hibi for the second time, having previously defeated the Japanese player 6-4, 6-1 in the first round of the Merida ITF W25 event in 2014. Hibi, who notched up her first WTA main draw win over Timea Babos on Monday, will bid for her third career Top 100 win - and first since 2013, when as a 17-year-old she beat Lauren Davis and Ajla Tomljanovic in a pair of ITF events.
No.6 seed Carla Suárez Navarro faces wildcard Bethanie Mattek-Sands on outdoor hard courts for the first time today. The pair have played three times previously, with Suárez Navarro taking their clay meeting 7-5, 6-2 in the first round of Bogota in 2008, and Mattek-Sands capturing both their indoor meetings, 6-0, 6-3 in the first round of Paris in 2011 and 6-3, 6-3 in the second round of Linz in 2012. Mattek-Sands' defeat of Venus Williams in the first round was the former World No.30's second singles win of her comeback from the knee injury she sustained at Wimbledon 2017, and first singles win since Roland Garros 2018.
ORDER OF PLAY
STADIUM (starts 11am)
[Q] Mayo HIBI (JPN) vs  Maria SAKKARI (GRE)
 Elina SVITOLINA (UKR) vs [WC] Daria KASATKINA (RUS)
Not before 3pm
[WC] CoCo VANDEWEGHE (USA) vs  Aryna SABALENKA (BLR)
Not before 7pm
 Carla SUÁREZ NAVARRO (ESP) vs [WC] Bethanie MATTEK-SANDS (USA)
Erin ROUTLIFFE (NZL) / Sabrina SANTAMARIA (USA) vs Ellen PEREZ (AUS) / Heather WATSON (GBR)
COURT 1 (starts 2pm)
Marie BOUZKOVA (CZE) / Priscilla HON (AUS) vs  Lyudmyla KICHENOK (UKR) / Nadiia KICHENOK (UKR)
Not before 4.30pm
Kristie AHN (USA) / Madison BRENGLE (USA) vs Monique ADAMCZAK (AUS) / Storm SANDERS (AUS)