Czech Karolina Pliskova is the first player to reach the semi-finals of the WTA season finals in Singapore.
The 26-year-old, who had already been in the preliminary round in the city-state last year, beat her compatriot Petra Kvitova 6-3, 6-4 on the third matchday of the White Group after 1-22 hours.
The two-time Wimbledon winner Kvitova, who lost for the first time in her fourth duel with Pliskova, leaves Singapore with a record of three defeats and 1:6 sets.
The final classification in the White Group will be decided by the second singles match of the day on Thursday: Elena Svitolina, who won her previous matches, would be first in the group ahead of Pliskova if she won against defending champion Caroline Wozniacki. If Switolina loses to the Dane in three sets, the relay victory goes to Pliskova ahead of the young Ukrainian. For Wozniacki, the only way into the preliminary round is to win two sets.
In the Red Group, Wimbledon winner Angelique Kerber (Kiel) fights on Friday against former US Open winner Sloane Stephens (USA) for a place in the semi-finals on Saturday. Kerber needs a two-set success to reach the final round of the season for the second time after 2016 without arithmetic games.
The tournament of the best eight players of the season, which will be held in Shenzhen, China, for ten years starting in 2019, is endowed with seven million dollars in prize money.