No.1 seed Ashleigh Barty and No.2 seed Karolina Pliskova have alternated wins over their five previous meetings, with Barty emerging as a 3-2 leader with victories in the 2012 Nottingham ITF 50K semifinals 2-6, 6-3, 7-6(6), 2017 Wuhan quarterfinals 4-6, 7-6(3), 7-6(2) and 2019 Miami final 7-6(1), 6-3. In between, Pliskova took their 2016 Nottingham quarterfinal 7-6(2), 7-6(7) and 2018 US Open fourth round 6-4, 6-4 - the only match in the series that has not involved a tiebreak.
No.7 seed Belinda Bencic leads the head-to-head against No.8 seed Elina Svitolina 2-1. Both of Bencic's victories came at landmark tournaments for the Swiss player: a 6-7(4), 6-4, 6-1 win in the third round of Charleston paved the way to her first WTA semifinal as a 17-year-old in just her seventh main draw - a run that lifted her into the Top 100 for the first time - and a 6-2, 3-6, 7-6(3) win in the Dubai semifinals in February came en route to Bencic's first title following several years of battling with injuries. However, Svitolina got a 6-2, 6-4 revenge in their most recent meeting, in the third round of Toronto this August.
Since the WTA Finals reverted to a round-robin format in 2003, two debutantes have made the semifinals on only two occasions - last year, with Sloane Stephens and Kiki Bertens, and this year, with Ashleigh Barty and Belinda Bencic.
Elina Svitolina is the first player to make it out of the group stages without dropping a set since Serena Williams in 2013, and is bidding to become the first defending champion to reach the final the following year - and to successfully defend the title - since Williams's hat-trick of victories between 2012 and 2014.
The semifinal between Ashleigh Barty and Karolina Pliskova will be the first meeting between the two highest-ranked players in the world since the 2018 Australian Open final, when World No.2 Caroline Wozniacki defeated World No.1 Simona Halep 7-6(2), 3-6, 6-4, and the first at the WTA Finals since the 2012 semifinals, when World No.2 Maria Sharapova defeated World No.1 Victoria Azarenka 6-4, 6-2.
ORDER OF PLAY (starts 4pm)
 Timea BABOS (HUN) / Kristina MLADENOVIC (FRA) vs  Samantha STOSUR (AUS) / ZHANG Shuai (CHN)
Not before 6.30pm
 Belinda BENCIC (SUI) vs  Elina SVITOLINA (UKR)
Not before 8pm
 Ashleigh BARTY (AUS) vs  Karolina PLISKOVA (CZE)
 HSIEH Su-Wei (TPE) / Barbora STRYCOVA (CZE) vs  Anna-Lena GROENEFELD (GER) / Demi SCHUURS (NED)