No.5 seed Simona Halep leads the head-to-head against No.8 seed Elina Svitolina 5-4 overall, including 2-1 on indoor hard courts. Indeed, the pair's first two meetings came indoors, with Halep winning 6-1, 6-1 in the 2013 Sofia Tournament of Champions round robin and 6-3, 7-5 in the 2014 Fed Cup Europe/Africa Zone Group I play-offs. They then alternated two wins on clay in 2017, Svitolina taking the Rome final and Halep saving a match point to avenge that loss three weeks later in the Roland Garros quarterfinals; following that, Svitolina reeled off three consecutive wins for the loss of just 13 games in the 2017 Toronto semifinals, 2017 WTA Finals round robin and 2018 Rome final. However, Halep has bounced back to win both of their clashes this year so far, capturing their Doha semifinal 6-3, 3-6, 6-4 and their Wimbledon semifinal 6-1, 6-3.
No.4 seed Bianca Andreescu is seeking to repeat the result of her only previous meeting with No.2 seed Karolina Pliskova, a 6-0, 2-6, 6-4 victory in the Toronto quarterfinals in August en route to her second title of 2019. Having started her career with eight consecutive wins over Top 10 players, the Canadian has now lost her last two - to Naomi Osaka in the Beijing quarterfinals and Simona Halep in her first round-robin match this week.
Today's advancement scenarios are as follows:
- Svitolina qualifies if she wins in straight sets on Wednesday. (Position in group tbd)
- If Svitolina and Pliskova win their matches on Wednesday, Svitolina qualifies as group winner and Andreescu is eliminated. (Pliskova and Halep would play for second spot Friday)
- If Halep and Andreescu win their matches on Wednesday, Halep qualifies as group winner and Pliskova is eliminated. (Svitolina and Andreescu would play for second spot Friday)
- Pliskova is eliminated if she loses in straight sets on Wednesday.
- Any other combination of results will mean qualification comes down to the final matches on Friday.
ORDER OF PLAY (starts 4pm)
 Elise MERTENS (BEL) / Aryna SABALENKA (BLR) vs  CHAN Hao-Ching (TPE) / Latisha CHAN (TPE)
Not before 6.30pm
 Simona HALEP (ROU) vs  Elina SVITOLINA (UKR)
Not before 8pm
 Karolina PLISKOVA (CZE) vs  Bianca ANDREESCU (ROU)
 Timea BABOS (HUN) / Kristina MLADENOVIC (FRA) vs  Anna-Lena GROENEFELD (GER) / Demi SCHUURS (NED)