ST. PETERSBURG, Russia — Australian Open finalist Petra Kvitova struggled with her serve and was eliminated from the St. Petersburg Ladies Trophy after losing to eighth-seeded Donna Vekic 6-4, 6-1 in the quarterfinals on Friday.
The second-ranked Kvitova landed only 48 percent of her first serves, double-faulted six times, and was broken five times.
Kvitova, the defending St. Petersburg champion who lost to Naomi Osaka in the Australian Open final, was playing in her 14th match in 24 days. It was Vekic's fifth match in that time.
Vekic will next face veteran Vera Zvonareva in the semifinals after she beat fellow Russian Daria Kasatkina 6-3, 7-6 (3).
The 12th-ranked Kasatkina has yet to win a match this year after four losses and a single walkover over the injured Maria Sharapova.
Fourth-seeded Aryna Sabalenka reached the semifinals by beating Russian qualifier Ekaterina Alexandrova 6-3, 6-4. She will next play Kiki Bertens, who beat Anastasia Pavlyuchenkova 6-2, 3-6, 6-0. That was a rematch after Pavlyuchenkova knocked Bertens out of the Australian Open second round.