Elena Rybakina easily defeated newcomer Ekaterina Alexandrova in the WTA Finals to sweep the group.
The sixth seed, who secured a spot in the semi-finals on Monday, continued his momentum with a 6-4 6-4 victory in Riyadh.
The Kazakh was scheduled to face Madison Keys, but the American failed to advance, withdrawing due to illness just hours before the start of the match.
Alexandrova was the second substitute but was given the nod after fellow Russian and first choice Mira Andreeva, who was also playing doubles in Riyadh, declared her unfit to play.
Rybakina, who defeated Amanda Anisimova and Iga Swiatek earlier this week, said: “Ekaterina is a difficult opponent to play against, especially in the early stages.”
“Of course I want to win every game I play and every win gives you confidence. Hopefully I can continue.”
Anisimova and Swiatek will compete for the second qualifying spot in the Serena Williams bracket later Wednesday.
The top eight women’s players in singles and doubles will compete in Saudi Arabia for a chance to win £12 million ($15.5 million).
In Stephanie Graf’s group, world No. 1 Aryna Sabalenka, Coco Gauff and Jessica Pegula all remain in contention for the semifinals.
Sabalenka will face defending champion Gauff in Thursday’s final round-robin match, while Pegula will play Jasmine Paolini, who has been eliminated.
