Top-ranked Kerber stunned by Russian teen11 January 2017 AFP, Sydney
Russian teenager Daria Kasatkina put Angelique Kerber's Australian Open preparations in a spin with a straight-sets upset win over the world number one at the Sydney International on Tuesday.
The 19-year-old, ranked 26, underlined her huge potential with a confident performance to take out the German, 7-6 (7/5), 6-2 in a second-round match played in sweltering conditions.
Only last week Kasatkina held a match point before going down to French Open champion Garbine Muguruza in the second round at the Brisbane International.
While she continues her march, Kerber's form is a concern ahead of next week's opening Grand Slam of the year, having also lost to Ukraine's Elina Svitolina 6-4, 3-6, 6-3 in the quarter-finals of the Brisbane International last week.
Kerber, who had a breakthrough 2016, winning two Grand Slams on her way to becoming world number one, struggled to find any rhythm and her usually strong forehand was astray.
Asked about her emotions after her biggest win yet, Kasatkina said courtside: "Difficult to explain because I beat the number one in the world and it doesn't happen every day. I think I got some confidence."
It was a day of upsets in Sydney where temperatures sizzled around 36 Celsius (97 Fahrenheit) with defending champion Svetlana Kuznetsova and last year's finalist Dominika Cibulkova both knocked out in the second round.
World number nine Kuznetsova went out to Russian compatriot Anastasia Pavlyuchenkova 7-5, 6-3 while Canada's Eugenie Bouchard continued her return to form with a 6-4, 6-3 win over the sixth-ranked Cibulkova.
Former Wimbledon finalist Bouchard, who has now won consecutive matches at a tournament for the first time since August, stretched her lead over Cibulkova to 4-1 head-to-head and will face Pavlyuchenkova in the last eight.
"Any time you play one of the best players in the world it's like a standard of where you're at," Bouchard said.
"I have taken a couple of solid steps this week, but I'm far from where I want to be. Even though I won, to me, I could do a lot of things better."