No.2 seed and 2015 runner-up Karolina Pliskova plays qualifier Kristina Mladenovic for the sixth time today. Pliskova leads the series 3-2, including a 6-1, 7-5 victory in the first round of the Australian Open one month ago. However, the pair are all square at 1-1 on outdoor hard courts - with Mladenovic taking one previous clash in Dubai, where she won their 2017 second-round meeting 6-2, 6-4.
Reigning US Open doubles champions Aryna Sabalenka and Elise Mertens face each other for the fifth time in singles, with the head-to-head currently all square at 2-2 (and 1-1 on outdoor hard courts). The pair have alternated wins so far: Mertens won their first meeting in the 2018 Lugano final 7-5 6-2 and their third 2-6, 7-6(1), 6-0 in the third round of Montréal 2018, saving one match point en route; Sabalenka took their second meeting 7-5, 2-6, 7-6(4) in the third round of Eastbourne 2018 and their most recent 6-4, 3-6, 7-5 in the 2019 Zhuhai round robin stages.
No.8 seed Petra Martic holds a 3-1 head-to-head lead over Barbora Strycova, including the last three. The pair played twice in 2011 and split meetings, with Strycova winning 6-4, 6-3 in Sydney qualifying and Martic taking their US Open first round 5-7, 6-3, 6-4. Seven years later, they played twice more in 2018, with the Croat winning both - in the second round of Indian Wells and first round of Beijing - in straight sets.
Elena Rybakina faces Katerina Siniakova for the second time in as many weeks, and for the fifth time in the past year. Rybakina's 6-3, 6-4 win in the first round of St. Petersburg last week levelled their head-to-head at 2-2, with the Kazakh having also been victorious in their first encounter 3-6, 6-2, 6-4 in the first round of Istanbul last year, while Siniakova took their Roland Garros first-rounder 7-6(5), 6-1 and their Guangzhou opener via retirement.
No.1 seed and 2015 champion Simona Halep's only previous encounter with wildcard Ons Jabeur took place in the first round of Beijing in 2018, and ended in Halep's retirement due to a back injury after losing the first set 6-1. The Tunisian will be bidding for a fourth career Top 10 win, and a career-best win by ranking over a completed match.
ORDER OF PLAY (all courts start 2pm)
[Q] Kristina MLADENOVIC (FRA) vs  Karolina PLISKOVA (CZE)
[Q] Veronika KUDERMETOVA (RUS) vs  Garbiñe MUGURUZA (ESP)
Elena RYBAKINA (KAZ) vs [Q] Katerina SINIAKOVA (CZE)
Not before 7pm
 Simona HALEP (ROU) vs [WC] Ons JABEUR (TUN)
Anett KONTAVEIT vs Anastasia PAVLYUCHENKOVA (RUS)
[Q] Jennifer BRADY (USA) vs Marketa VONDROUSOVA (CZE)
 Petra MARTIC (CRO) vs Barbora STRYCOVA (CZE)
Elise MERTENS (BEL) vs  Aryna SABALENKA (BLR)
 Barbora KREJCIKOVA (CZE) / ZHENG Saisai (CHN) vs [WC] Caroline GARCIA (FRA) / Sania MIRZA (IND)
Desirae KRAWCZYK (USA) / Alison RISKE (USA) vs  CHAN Hao-Ching (TPE) / Latisha CHAN (TPE)
 Gabriela DABROWSKI (CAN) / ZHANG Shuai (CHN) vs Karolina MUCHOVA (CZE) / Marketa VONDROUSOVA (CZE)
 HSIEH Su-Wei (TPE) / Barbora STRYCOVA (CZE) vs HAN Xinyun (CHN) / PENG Shuai (CHN)
Makoto NINOMIYA (JPN) / YANG Zhaoxuan (CHN) vs  Nicole MELICHAR (USA) / XU Yifan (CHN)
Karolina PLISKOVA (CZE) / Kristyna PLISKOVA (CZE) vs Hayley CARTER (USA) / Luisa STEFANI (BRA)
Lyudmyla KICHENOK (UKR) / Nadiia KICHENOK (UKR) vs  DUAN Yingying (CHN) / Veronika KUDERMETOVA (RUS)
Sofia KENIN (USA) / Bethanie MATTEK-SANDS (USA) vs  Kveta PESCHKE (CZE) / Demi SCHUURS (NED)