No.9 seed Belinda Bencic was unable to take a set off No.7 seed and 2014 runner-up Petra Kvitova across their first three meetings, in the second round of Tokyo 2013, their Fed Cup first-round rubber in 2018 and in the third round of this year's Australian Open. However, the Swiss No.1 - who owns a Tour-leading nine Top 10 wins in 2019 - finally captured her first win in the series 6-3, 1-6, 6-2 in the Dubai final in February.
No.3 seed Elina Svitolina and No.15 seed Sofia Kenin will play each other for the fourth time, with all their meetings coming on hard courts this season. Svitolina, a 2016 semifinalist in Beijing, squeezed past Kenin the first time 3-6, 7-6(5), 6-4 in the second round of Indian Wells in March, but the American triumphed in consecutive weeks in August - 7-6(2), 6-4 in the Toronto quarterfinals and 6-3, 7-6(3) in the third round of Cincinnati.
No.5 seed Bianca Andreescu faces a rematch of her US Open quarterfinal a month ago against Elise Mertens, the only time the pair have played before. Andreescu won it 3-6, 6-2, 6-3 en route to lifting her maiden Grand Slam trophy. Mertens is seeking her first Top 10 victory since winning three back-to-back to take the Doha title in February.
No.1 seed Ashleigh Barty dominates the head-to-head against Zheng Saisai 4-0, including a 6-4, 6-2 win in their most recent meeting, in the first round of Wimbledon this year. Zheng, the only Chinese player remaining in the draw, has twice managed to win the opening set, including in their only previous hardcourt encounter in the second round of Wuhan last year, which Barty eventually took 4-6, 6-1, 6-2.
In an all-American derby, qualifier Jennifer Brady will bid for her fourth Top 20 win of 2019 over No.11 seed and 2016 semifinalist Madison Keys. All previous three were over Caroline Garcia, whom Brady upset in Hua Hin, Dubai and Indian Wells.
Polona Hercog will look to score consecutive Top 20 victories for the first time in her career against No.8 seed Kiki Bertens. Hercog, whose upset of No.10 seed Angelique Kerber was her second Top 20 win of 2019, will also look to improve a 1-27 record against Top 10 opposition; the Slovenian's sole win was over Marion Bartoli in the third round of Charleston 2012.
ORDER OF PLAY (all courts start 12.30pm)
After 1 ATP match, not before 2.30pm
 Bianca ANDREESCU (CAN) vs Elise MERTENS (BEL)
 Ashleigh BARTY (AUS) vs ZHENG Saisai (CHN)
After 1 ATP match, not before 9pm
 Elina SVITOLINA (UKR) vs  Sofia KENIN (USA)
[Q] Jennifer BRADY (USA) vs  Madison KEYS (USA)
After 2 ATP matches, not before 6pm
 Belinda BENCIC (SUI) vs  Petra KVITOVA (CZE)
Polona HERCOG (SLO) vs  Kiki BERTENS (NED)
 HSIEH Su-Wei (TPE) / Barbora STRYCOVA (CZE) vs Jelena OSTAPENKO (LAT) / Dayana YASTREMSKA (UKR)
[WC] PENG Shuai (CHN) / WANG Yafan (CHN) vs  Timea BABOS (HUN) / Kristina MLADENOVIC (FRA)
 Gabriela DABROWSKI (CAN) / XU Yifan (CHN) vs Karolina PLISKOVA (CZE) / Kristyna PLISKOVA (CZE)
 CHAN Hao-Ching (TPE) / Latisha CHAN (TPE) vs Shuko AOYAMA (JPN) / Ena SHIBAHARA (JPN)
After 1 ATP match
 Anna-Lena GROENEFELD (GER) / Demi SCHUURS (NED) vs Ekaterina ALEXANDROVA (RUS) / Katerina SINIAKOVA (CZE)
Julia GOERGES (GER) / Anastasija SEVASTOVA (LAT) vs  Nicole MELICHAR (USA) / Kveta PESCHKE (CZE)