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 overtaken Konta by winning the Kremlin Cup but she retired in the second round.
Konta remains in line to take the last place at the eight-player season-ending event, but the Briton is not competing this week as she recovers from injury.
Kuznetsova, who also needs to win the title, beat Alize Cornet 6-4 7-5.
The Russian, who is the defending champion, will play Kristina Mladenovic or Timea Babos in the quarter-finals on Thursday.