World number one Angelique Kerber's Australian Open preparations suffered another setback, beaten by Daria Kasatkina at the Sydney International.

The German, runner-up at the WTA Premier event in 2014, went down to talented Russian Kasatkina 7-6 (7-5) 6-2 in the second round.

For Kerber, it added to a quarter-final exit in Brisbane as she prepares to defend her title at Melbourne Park.

Kasatkina, the world number 26, broke serve five times to win in one hour, 32 minutes.

Kerber served six double faults in her loss, continuing a below-par start to the year for the two-time grand slam champion.

Kasatkina, 19, will face either Daria Gavrilova or Johanna Konta in the quarter-finals.

It continued a day of upsets in Sydney, where Dominika Cibulkova and defending champion Svetlana Kuznetsova were also eliminated.