Sydney — Eight of the top 10 women in tennis are injured or have become sick in the lead up to the Australian Open, the latest being Angelique Kerber after she withdrew from the Sydney International on Tuesday with a stomach illness.

Kerber lost in the final of last week's Brisbane International to Victoria Azarenka and beat Elina Svitolina in the first round in Sydney before falling ill and pulling out of her second-round match against Ekaterina Makarova on Tuesday.

"I'm very sorry I can't go on court today but I'm not feeling 100 percent," Kerber said. "I don't want to risk my health before Melbourne, of course, but I love to come back to the Apia International Sydney and always have good results here - semifinals last year and the final two years ago."

The Sydney tournament has already lost fourth-ranked Agnieszka Radwanska to a leg injury and defending champion Petra Kvitova, ranked No. 6, to a stomach virus, along with Daria Gavrilova of Australia, winner of last week's Hopman Cup, who has an abdominal strain.

Last week, four other top-ranked women either retired or withdrew from tournaments because of injuries: No. 1 Serena Williams (Hopman Cup/knee), second-ranked Simona Halep (Brisbane/ankle), No. 3 Garbine Muguruza (Brisbane/foot) and No. 5 Maria Sharapova (Brisbane/forearm).

Ninth-ranked Lucie Safarova has already withdrawn from the Australian Open with a bacterial infection, leaving No. 10 Venus Williams as the only active member of the women's top 10 without an injury concern or illness ahead of the tournament, which starts Monday.

Halep showed signs of improvement, shrugging off the Achilles tendon problem that forced her out of the Brisbane International to beat Caroline Garcia 6-4, 2-6, 6-2 in the second round and move into the quarterfinals in Sydney, where she is seeded No. 1.

Earlier Tuesday, Sara Errani rallied from 5-1 down in the second set, saving seven set points, to beat former No. 1 Jelena Jankovic 7-6 (3), 7-6 (8) to advance to the quarterfinals.

"Yeah, it was 5-1, but I had many games with 40-Love, 40-15, and advantage, and so it didn't really feel like 5-1," Errani said. "I was just thinking that I was near my best level, and to just try to keep going, play all the points, and finally was 5-all, and 5-5, 6-all, and really tough the tiebreaker."

Fifth-seeded Karolina Pliskova beat Anastasia Pavlyuchenkova 6-3, 6-0 and eighth-seeded Belinda Bencic defeated Tsvetana Pironkova 6-3, 6-3.

Samantha Stosur also reached the Sydney quarterfinals for the first time in 11 years when she beat Slovakian veteran Daniela Hantuchova 6-4, 6-2. Stosur was runner-up at the tournament in 2005.

In the men's draw, Teymuraz Gabashvili beat seventh-seeded Leonardo Mayer 6-4, 6-3, eighth-seeded Alexandr Dolgopolov beat Thomaz Bellucci 6-1, 6-4 and Nicolas Mahut beat Adrian Mannarino 6-4, 7-5.

At the Hobart International, Eugenie Bouchard continued her injury comeback with a 6-4, 7-5 win over Alison Van Uytvanck. She is playing in only her third tournament since she sustained a concussion when she fell in the dressing room at the U.S. Open in September. Bouchard also reached the quarterfinals of last week's Shenzhen Open.

"I just felt my timing was a bit off and my serve was definitely not there so at least I pulled through, but I definitely want to be able to play better than that," the Canadian said.

Second-seeded Camila Giorgi beat Nao Hibino 6-2, 6-3 to reach the quarterfinals.

On a rain-shortened day at the ASB Classic in Auckland, New Zealand, eighth-seeded Robert Bautista Agut beat defending champion Jiri Vesely 6-3, 7-5 and 2008 champion Philipp Kohlschreiber beat Benjamin Becker 7-6 (8), 6-3.

Sam Querrey and Aljaz Bedene had been locked in a marathon match before Bedene was forced to retire while trailing 6-7 (5), 7-6 (10), 2-1 after nearly two hours.