BASTAD, Sweden (AP) Defending champion Mona Barthel struggled past local wild card Rebecca Peterson 6-1, 7-6 (3) to secure a spot in the Swedish Open semifinals on Friday.
Kazakhstan's Yulia Putintseva reached her first career WTA semifinal when she beat Czech player Klara Koukalova 6-3, 6-4.
Koukalova, the doubles champion in 2013, advanced to the quarterfinals by a walkover on Thursday when Serena Williams withdrew with a right elbow injury.
Lara Arruabarrena of Spain was into her second semi of the year by topping Jana Cepelova 6-3, 5-2 after the Slovak retired with a neck injury.
In the last quarterfinal, local hope and seventh seed Johanna Larsson beat third-seeded Barbora Strycova of the Czech Republic 6-2, 6-3. Larsson will meet Putintseva on Saturday, and Barthel faces Arruabarrena.