Sydney: Angelique Kerber's build-up for next week's Australian Open suffered a setback when the world No. 1 was beaten 7-6 (5), 6-2 by Russian teenager Daria Kasatkina in the second round of the Sydney International on Tuesday.
An error-prone Kerber struggled to reproduce the form that led her to a first Grand Slam triumph at Melbourne Park last year and came unstuck against the 19-year-old Kasatkina.
"The first matches of the year are always tough and I still don't feel my rhythm. I made too many mistakes," Kerber, who also lost in the quarter finals in Brisbane last week, said of her 41 unforced errors.
Anastasia Pavlyuchenkova earlier won an all-Russian battle against Svetlana Kuznetsova. Pavlyuchenkova beat world No. 9 and defending champion Kuznetsova 7-5, 6-3 to set up a quarter-final clash against Canadian Eugenie Bouchard who caused another upset by defeating third seed Dominika Cibulkova.
Ninth seed Italian Robert Vinci also fell to Czech Barbora Strycova 6-2, 6-3 but former world No. 1 Caroline Wozniacki bucked the trend with a 6-0, 7-5 win over Kazakh Yulia Putintseva.