Moscow - Australian Open champion and world No 1 Caroline Wozniacki lost 7-6 (7/2), 6-3 to local player Daria Kasatkina in the quarter-finals of the St Petersburg Ladies Trophy on Friday.
Fresh from her first ever Grand Slam title the Dane had raced to the quarter-finals here but had been expecting the Russian to give her a difficult time.
"It's gonna be difficult but I'm excited for it," the 27-year-old said ahead of he clash with the sixth seed Kasatkina.
Fourth seed and Defending champion Kristina Mladenovic of France made an important step to retaining her title with a straight-sets win over Czech Katerina Siniakova on Friday.
Mladenovis, ranked 10th in the world, prevailed 6-4, 6-3 to book a semi-final spot and to record her second win over the 21-year-old Siniakova in their fifth head-to-head meeting.
Mladenovic will face Kasatkina.
"It was a very good match as she (Siniakova) has been on great all season," Mladeniovic said on-court after the match. "I'm very happy with the intensity that I've put into the game today.
"No doubts the semi-final will be extremely difficult as Dasha (Kasatkina) is such a talented youngster and she always plays at her top in front of her home crowd."
Meanwhile, Czech two-time former Wimbledon champion Petra Kvitova cruised comfortably into the last four losing just two games in her 58-minute match with reigning French Open champion Jelena Ostapenko of Latvia 6-0, 6-2.
In the match for a place in the final Kvitova, who appeared in the main draw courtesy of a wild card, will clash with Germany's Julia Goerges, who ousted another Russian Elena Rybakina 6-3, 6-3.
"At this tournament every opponent is very hard to beat and I will need to show my best tennis to win the semi-final," Goerges said.
Results from the WTA Saint Petersburg Trophy on Friday (x denotes seed):
Darya Kasatkina (RUS x8) bt Caroline Wozniacki (DEN x1) 7-6 (7/2), 6-3
Kristina Mladenovic (FRA x4) bt Katerina Siniakov (CZE) 6-4, 6-3
Julia Goerges (GER x5) bt Elena Rybakina (RUS) 6-3, 6-3
Petra Kvitova (CZE) bt Jelena Ostapenko (LAT x2) 6-0, 6-2