Reigning World No.1 Caroline Wozniacki was shocked by Russia's Daria Kasatkina in straight sets in the quarter-finals of the St Petersburg Ladies Trophy.
Wozniacki, who recently won the Australian Open, her first Grand Slam, lost 7-6 (7/2), 6-3 to local player Kasatkina.
Eighth-seed Kasatkina scored her second career win over a reigning World No.1, having beaten Angelique Kerber last season in Sydney.
The Russian will next meet defending champion Kristina Mladenovic in the semi-final clash, who booked her spot in the last four after beating Katerina Siniakova 6-4, 6-3.