Top-10 stars Anett Kontaveit and Paula Badosa clocked wins to open their Sydney Classic campaigns Monday but world number one Ashleigh Barty pulled out to rest ahead of the Australian Open.

Estonian world number seven Kontaveit swept past China's Zhang Shuai 6-3, 6-3 while Spain's ninth-ranked Badosa overcame Latvia's Jelena Ostapenko 7-6 (7/1), 6-1.

But former Australian Open champion Sofia Kenin, ranked 12, crashed at the first hurdle 6-4, 6-0 to Russia's Daria Kasatkina.

Two-time Wimbledon champion Petra Kvitova, meanwhile, survived a scare against Arantxa Rus, battling back from a set down to win 3-6, 7-6 (7/4), 7-5.

Czech Kvitova was stunned by Australian Priscilla Hon at Adelaide last week, but Hon couldn't repeat that form as she lost her Sydney opener in straight sets to Romania's Jaqueline Cristian.

The in-form Kontaveit ended her 2021 season by winning 29 of her last 34 matches, and she picked up where she left off against Zhang in her 2022 debut.

"I think I have this inner confidence but I'm not putting too much pressure on myself," she said.

"The end of the season was physically very demanding and although now I'm feeling good and ready to play again, it's going to be a new season and just really happy to be back competing."

Top seed Barty pulled out after clinching the singles and doubles titles at the Adelaide International, opting instead to travel directly to Melbourne for the opening Grand Slam of the year, which starts next week.

"Unfortunately, I am withdrawing from the Sydney Tennis Classic to have some time to recover before the Australian Open," she said.

Barty demolished Kazakhstan's Elena Rybakina 6-3, 6-2 to claim the 14th singles title of her career on Sunday, then returned to win the doubles with Storm Sanders.

It was her first tournament in four months, since a shock third-round loss at the US Open in September, after which she opted to remain in Australia because of the pandemic.

Former French Open champion Iga Swiatek, who fell to Barty in the Adelaide semis, also withdrew from Sydney.

"After a tense pre-season and last week's tournament in Adelaide I feel like my body needs more time to recover before @australianopen," the Pole tweeted, adding that she had some pain in her lower rib area.

Swiatek was due to open her Sydney tournament against US Open champion Emma Raducanu, who missed the Melbourne Summer Set event last week as she continued to recover from coronavirus. 

The Briton will instead play Rybakina.

Among the men, Belgium's David Goffin won his first-round match 6-4, 6-4 against Argentina's Facundo Bagnis, while Australian Jordan Thomson, Italy's Lorenzo Sonego and Finland's Harri Heliovaara were also winners.

But Australian Nick Kyrgios withdrew after contracting Covid-19, putting his Australian Open campaign in doubt.