Johanna Konta can only be overtaken by Svetlana Kuznetsova in the race to qualify for the WTA Finals, after Carla Suarez Navarro's hopes ended in Moscow.
Suarez Navarro could have passed Konta by winning the Kremlin Cup but retired with a wrist injury in round two.
Konta is in line to take the eighth and final place at the season-ending event, but the Briton is not competing this week as she recovers from injury.
Kuznetsova, who needs to win the Kremlin Cup, beat Alize Cornet 6-4 7-5.
The Russian, who is the defending champion, will play Hungary's Timea Babos in the quarter-finals on Thursday.
"I try not to think about it," said Kuznetsova. "It's a tough goal - I have to win the Kremlin Cup, meaning it's a long way to go. I will do my best."
Konta, 25, is eighth in the Singapore standings following the withdrawal of world number two Serena Williams, but it is not clear whether the Briton would be fit to play should she qualify.
|Road to Singapore (*470 points awarded for Moscow title)|
|1. Angelique Kerber (Germany) - Qualified|
|2. Agnieszka Radwanska (Poland) - Qualified|
|3. Simona Halep (Romania) - Qualified|
|4. Karolina Pliskova (Czech Republic) - Qualified|
|5. Garbine Muguruza (Spain) - Qualified|
|6. Madison Keys (USA) - Qualified|
|7. Dominika Cibulkova (Slovakia) - Qualified|
|8. Johanna Konta (Great Britain) - 3455 points|
|9. Carla Suarez Navarro (Spain) - 3170 points|
|10. Svetlana Kuznetsova (Russia) - 3080 points*|