Serena steps up defence

Serena Williams stepped up the defence of her Australian Open title with a crushing straight sets third-round win over 32nd seed Carla Suarez Navarro.

The world number one is a four-time winner at Melbourne Park but she has never successfully defended her title. The American is on course to change that after over-powering the Spaniard 6-0 6-3.

Williams was also joined in the last-16 by her elder sister Venus, who fended off the plucky challenge of Australia's Casey Dellacqua 6-1 7-6 (7/4).

The 28-year-old is, however, expecting a tough challenge in the next round where she will meet Sam Stosur, a 6-4 6-1 winner over Alberta Brianti.

The Australian beat Williams when they last met in Los Angeles last year and with her home crowd behind her the defending champion is wary of her threat.

"She beat me the last time we played, so she has a lot of momentum. I definitely expect the crowd to root for Sam. I mean, I would," said Serena Williams.

Venus Williams will face 17th seed Francesca Schiavone next after she upset Agnieszka Radwanska, the 10th seed, 6-2 6-2.

Seventh seed Victoria Azarenka has quietly made her way through the draw, but confirmed she is a threat with a 6-0 6-2 win over unseeded 32-year-old Tathiana Garbin 6-0 6-2.

It was the third consecutive match in which the Belorussian has claimed a set to love and she will next play ninth-seeded Russian Vera Zvonareva who easily overcame Gisela Dulko 6-1 7-5.

China's Li Na was the only unseeded player to go through as she upset 22nd seed Daniela Hantuchova 7-5 6-3 6-2. Li will pay the winner of Saturday's match between fourth seed Caroline Wozniacki and Shahar Peer (29) in the last-16.