'It's difficult to explain really. I beat the number one in the world and it doesn't happen every day. I think I will get some confidence.'
Angelique Kerber's build-up for next week's Australian Open suffered a setback with the German world number one going down in straight sets to Russian teenager Daria Kasatkina in the second round of the Sydney International on Tuesday.
On a manic day for the seeded players, the 19-year-old Kasatkina won 7-6(5), 6-2 against two-time Grand Slam winner Kerber, who also in the quarter-finals in Brisbane last week.
"It's difficult to explain really. I beat the number one in the world and it doesn't happen every day," Kasatkina, ranked 26 in the world, said in a courtside interview.
"I think I will get some confidence," she said referring to the year's first Grand Slam, starting on Monday in Melbourne, where Kerber would defend her women's title.
Anastasia Pavlyuchenkova earlier won an all-Russian battle against Svetlana Kuznetsova to oust the defending champion in straight sets.
Pavlyuchenkova beat world number nine Kuznetsova 7-5, 6-3 to set up a quarter-final clash against Canadian Eugenie Bouchard who caused another upset by defeating number three seed Dominika Cibulkova.
Ninth seed Italian Robert Vinci also fell to Czech Barbora Strycova 6-2, 6-3 but former world number one Caroline Wozniacki bucked the trend with a 6-0, 7-5 win over Kazakh Yulia Putintseva.
Pavlyuchenkova came into the match having lost five of the last six meetings against Kuznetsova and twice fell back in the opening set.
The 31-year-old double Grand Slam winner was serving for the set at 5-4 before Pavlyuchenkova reeled off the last three games to bag the set.
"I'm really happy, especially because she's not only defending champion but my fellow (countrywoman) and she's top 10 and she's had a really incredible year last year," Pavlyuchenkova said.
"I think I did everything well. I wasn't serving as well as I did yesterday; I was a little upset with that, but I'm so happy that even with a lower first serve percentage, that I was able to win the match in two sets."
Next up for the Russian will be former Wimbledon finalist Bouchard who completed her fourth consecutive hard-court win against world number six Cibulkova with a 6-4, 6-3 victory.
It will be the first WTA quarter-final appearance for the Canadian in 10 months since Kuala Lumpur, where she lost in the final of the Malaysian Open.
"Any time you play one of the best players in the world... it's like a standard of where you're at," Bouchard said after taking her head-to-head record over Cibulkova to 4-1.
Sharapova to return from ban in Stuttgart
Five-time grand slam champion Maria Sharapova will return to competitive action following a 15-month doping ban at the Stuttgart Grand Prix in April.
The Florida-based Russian was originally banned for two years after testing positive for meldonium at last year's Australian Open.
The former world number one admitted she had used meldonium for years and was not aware it had been banned since the start of 2016. Her suspension was later cut to 15 months on appeal.
"I could not be happier to have my first match back on tour at one of my favourite tournaments," Sharapova, who won the indoor clay event three years running from 2012, said on the tournament website.
"I can't wait to see all my great fans and to be back doing what I love."
She will return to action in time to contest the season's second grand slam at Roland Garros. The French Open begins on May 22.