Ana Ivanovic will play US Open finalist Roberta Vinci in the semi-finals of the St Petersburg Ladies Trophy.
Fourth seed Ivanovic has had a disappointing start to 2016 but is enjoying a good week in Russia and ended the run of qualifier Kateryna Kozlova 6-1 7-5.
Vinci was given a real battle by Hungary's Timea Babos but came through 7-6 (7/3) 4-6 7-6 (7/4) after two hours and 33 minutes.
In the other semi-final, the top-seeded Belinda Bencic will face 18-year-old Russian Daria Kasatkina.
World number 11 Bencic, of Switzerland, overcame Russia's Anastasia Pavlyuchenkova 6-7 (7/4) 6-4 6-2 in a two-and-a-half-hour match that ended after midnight in St Petersburg.
Kasatkina had earlier overcome Slovakia's Dominika Cibulkova 4-6 7-5 6-3.
Source: PA
