The current world no 8 joined Maria Sakkari, Ekaterina Alexandrova and Elena Rybakina in the semifinal of the tournament.
Kiki Bertens defeated Anastasia Potapova 6-4, 7-6(3) in two sets to secure herself a place in the semifinal of the St. Petersburg Ladies' Trophy.
Bertens won the first set with relative ease but faced a rujuvenated Potapova in the second set. The Russian upped her game after losing to first set and gave Bertens a hard time.
The 28-year-old had to fight back from a 5-2 deficit in the second set and save three set points. And the match would go to deuce seven times.
The world no 8 held her own as Potapova continued to launch shots at her. Overall, Bertens saved 14 break points, won the second set and is one course to defend her title.
The Dutch will face another Russian for the third straight match as she takes on Ekaterina Alexandrova in the semifinal. The other two Russians Bertens have played are Potapova and Veronika Kudermetova.
And tomorrow's semifinal tie is the first time Bertens and Alexandrova are playing each other.
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