In five previous meetings, No.8 seed Elina Svitolina has conceded no losses and just two sets to No.1 seed Ashleigh Barty. Those dropped sets came in their first encounter, and only previous on indoor hard courts, in Fed Cup World Group II action, which Svitolina won 4-6, 6-1, 6-2; and in their most recent clash, a three-hour, 12-minute marathon in the fourth round of Indian Wells this year - the sixth-longest match of the season - taken by the Ukrainian 7-6(8), 5-7, 6-4. In between, Svitolina also posted straight-sets defeats of Barty at Wimbledon and Beijing in 2017, and at Miami 2018.
Svitolina is bidding to become the seventh player to successfully defend a WTA Finals title, following Chris Evert (1972-73), Martina Navratilova (who defended the title five times in total between 1979 and 1986), Monica Seles (who won a hat-trick of trophies between 1990 and 1992), Stefanie Graf (1995-96), Kim Clijsters (2002-03), Justine Henin (2006-07) and Serena Williams (who won a hat-trick between 2012 and 2014). The Ukrainian already has three successful title defences under her belt in her career: Baku 2013-14, Dubai 2017-18 and Rome 2017-18.
Barty is aiming to become the seventh player to lift the WTA Finals trophy on her debut in the tournament, following Chris Evert (who won the first edition of the event in 1972), Evonne Goolagong Cawley (1974), Serena Williams (2001), Maria Sharapova (2004), Petra Kvitova (2011) and Dominika Cibulkova (2016).
Svitolina is seeking her first title since winning the WTA Finals at the end of 2018, in her first final of the 2019 season. Barty, meanwhile, has reached a Tour-leading sixth final of the year, and a title would tie her with Karolina Pliskova for a Tour-leading four trophies.
Barty is looking to become the second Australian champion at the WTA Finals following 1974 and 1976 winner Evonne Goolagong Cawley. The last time either a World No.1 or reigning Slam champion took the title was Serena Williams's 2014 victory.
In the doubles final, No.2 seeds Hsieh Su-Wei and Barbora Strycova defeated No.3 seeds Timea Babos and Kristina Mladenovic 7-6(5), 6-4 in their only previous meeting in this year's Wimbledon semifinals.
Babos and Mladenovic are aiming to become the sixth team to successfully defend a WTA Finals title, following Martina Navratilova and Pam Shriver (who defended the trophy a total of seven times between 1982 and 1989), Gigi Fernandez and Natasha Zvereva (1993-94), Martina Hingis and Anna Kournikova (1999-2000), Lisa Raymond and Samantha Stosur (2005-06) and Cara Black and Liezel Huber (2007-08). Babos, who was also the 2017 champion alongside Andrea Sestini Hlavackova, would also be the fourth player to win a consecutive hat-trick of titles at this tournament following Navratilova, Shriver and Lindsay Davenport (1996-98 partnering Mary Joe Fernandez, Jana Novotna and Zvereva).
ORDER OF PLAY (starts 4.30pm)
 Timea BABOS (HUN) / Kristina MLADENOVIC (FRA) vs  HSIEH Su-Wei (TPE) / Barbora STRYCOVA (CZE)
Not before 7.30pm
 Ashleigh BARTY (AUS) vs  Elina SVITOLINA (UKR)