Top-seeded Elina Svitolina has squandered her opening match at the Kremlin Cup after having been a break up in the deciding set.
Veronika Kudermetova beat the fourth-ranked Svitolina, who had a first-round bye, 6-2 1-6 7-5 in their second-round match to set up a quarter-final with either Anastasia Pavlyuchenkova or wild-card entry Varvara Gracheva.
Also Thursday, second-seeded Kiki Bertens continued her push to reach the season-ending WTA Finals by beating Kaia Kanepi 4-6 6-3 7-5.
Both Bertens and Belinda Bencic can take the last WTA Finals spot from Serena Williams if they reach the final in Moscow, where they are in the same half of the draw.