Sydney: World No. 6 Karolina Pliskova has withdrawn from the Sydney International with a left thigh injury, tournament organisers said on Sunday.

The Czech, who was the fourth seed for the Sydney event, demolished France’s Alize Cornet 6-0, 6-3 to win the Brisbane International on Saturday.

As her withdrawal came before the start of the first match, Italian Roberta Vinci as the next eligible seed took Pliskova’s open spot and a qualifier/lucky loser would come into the draw, organisers said.

Pliskova is set to leapfrog Dominika Cibulkova to become world No. 5 when the new rankings are released on Monday.

Pliskova is one of the favourites for the Australian Open, which begins in Melbourne next week.

She was runner-up to world No. 1 Angelique Kerber at last year’s US Open.

Ukraine’s world No. 14 Elina Svitolina later became the second top-ranking player to withdraw from the tournament, citing a viral illness.

“I’ve had constant headaches for the last two days and unfortunately in today’s hot weather it got even worse when I was warming up and my body wasn’t ready to compete,” Svitolina said.

The next eligible seed Denmark’s Caroline Wozniacki takes the open spot and will face Monica Puig of Puerto Rico on Monday.

Svetlana Kuznetsova opened the defence of her Sydney title with a comfortable 6-1 6-4 victory over Irina-Camelia Begu. The Russian fifth seed started strongly by winning 10 of the first 11 games and after her Romanian opponent rallied in the second set to tie it up at 4-4, Kuznetsova broke again in the ninth game and served out the victory in 77 minutes.

“I started the year quite good with the feeling,” the 31-year-old double grand slam winner told reporters.

“Sometimes the results don’t go together with whatever you feel. But I feel very good for the start of the year, and for me it’s a very nice feeling.

“I never thought of defending my title or something like that. It’s just another tournament — the title I have at home and no-one will take it away from me. This is another year and another opportunity to play.” Kuznetsova will next face the winner of the match between local favourite Sam Stosur and fellow Russian Anastasia Pavlyuchenkova.

Elsewhere, Canada’s Eugenie Bouchard, a former Wimbledon finalist, also won her opening match with a 7-6(1) 6-2 first round win over China’s Zhang Shuai.