SYDNEY (AP) — Top-ranked Angelique Kerber lost her opening match at the Sydney International on Tuesday, upset 7-6 (5), 6-2 by Darya Kasatkina in a setback ahead of her Australian Open title defense next week.
Kerber, who won last year's Australian and U.S. Open for her first major titles, has opened the new season with one win in two tournaments in Brisbane and Sydney. The Australian Open starts Monday in Melbourne.
"The first matches of the year are always tough, and I'm still not feeling my rhythm," Kerber said. "I made too many mistakes. I was not feeling the ball.
"It's the second tournament of the year. We have still a lot to go, so I will not do a big drama about that match."
Kasatkina broke Kerber's serve five times and registered her first win ever against a top five player.
"Difficult to explain because I beat No.1 in the world and . doesn't happen every day," the 19-year-old Russian said when asked about her emotions after the career-high win. "I think I get some confidence."
She moved into a quarterfinal against sixth-seeded Johanna Konta, who beat Daria Gavrilova 6-1, 6-3
Eugenie Bouchard continued her resurgent run heading into the season's first major with a 6-4, 6-3 win over WTA Finals champion Dominika Cibulkova to reach the quarterfinals in Sydney.
Bouchard improved her career record to 4-1 against Cibulkova, who was ranked No. 5 and was voted the WTA's comeback player of the year in 2016 after her title win at the season-ending championship.
"Any time you play one of the best players in the world it's like a standard of where you're at," said Bouchard, who had a wild-card entry in Sydney. "Every time I have played a match with Domi, we have had the toughest battles.
"I have won, I guess, more often than not, but everyone is a really tough battle."
Bouchard had an early break in the second set, but dropped serve and allowed Cibulkova, a finalist at the 2014 Australian Open, a way back into the match.
But the Canadian star broke again quickly and held onto the advantage, and later attributed her recent improvement to a reunion with coach Thomas Hogstedt.
Bouchard had a breakout season in 2014, reaching the semifinals at the Australian Open and French Open before making the final at Wimbledon. But she has only gone past the fourth round at a major once since then and slipped to No. 46 at the end of last year.
After winning back-to-back matches at a tournament for the first time since August in Cincinnati, she will play a quarterfinal against Anastasia Pavlyuchenkova, who beat defending champion Svetlana Kuznetsova 7-5, 6-3.
"I have taken a couple of solid steps this week, but I'm far from where I want to be," Bouchard said. "Even though I won, to me, I could do a lot of things better."
Former No. 1-ranked Caroline Wozniacki beat Yulia Putintseva 6-0, 7-5 to move into a quarterfinal against Barbora Strycova, who ousted No. 9-seeded Roberta Vinci 6-2, 6-3.
No. 2-ranked Agnieszka Radwanska had a 7-6 (1), 6-1 win over Christina McHale and will next play Chinese qualifier Duan Yingyang, who beat Coco Vandeweghe 6-3, 6-2 to make the quarterfinals.
In men's first-round matches, Alex De Minaur beat Benoit Paire 6-3, 3-6, 7-6 (1), Andrey Kuznetsov was leading 2-6, 6-1, 3-0 when No. 7-seeded Martin Klizan retired, and No. 6 Gilles Muller advanced over Alexandr Dolgopolov.
At the Hobart International, third-seeded Monica Niculescu moved into the quarterfinals by beating Kirsten Flipkens 6-3, 6-2, and Veronica Cepede Royg had a 6-3, 0-6, 6-4 win over Andrea Petkovic.
At the ASB Classic in Auckland, New Zealand, fifth-seeded Spaniard Albert Ramos-Vinola lost 6-1, 7-5 in the first round to friend and training partner Joao Sousa, and No. 8-seeded Marcos Baghdatis beat Adrian Mannarino 6-4, 6-4.
Ramos-Vinola, ranked 27, and Portugal's Sousa, ranked 44, are both based in Barcelona and are supporters of the city's rival football clubs and Sousa described their match as "a kind of a derby."
"On court we are no friends but off court we are," he said.