MELBOURNE: Novak Djokovic and Venus Williams strode into the Australian Open quarter-finals Monday while Li Na ensured China has two players in the last eight of a Grand Slam for the first time.

Third seed Djokovic, the 2008 winner, joins Spanish defending champion Rafael Nadal, British fifth seed Andy Murray, American seventh seed Andy Roddick and 14th seeded Croat Marin Cilic safely through.

Also staying in the hunt was in-form Russian sixth seed Nikolay Davydenko, who was stretched to the limit by Spanish ninth seed Fernando Verdasco before prevailing 6-2, 7-5, 4-6, 6-7 (5/7), 6-3.

Roger Federer attempts to join them later Monday with the 15-time Grand Slam champion playing Australia's Lleyton Hewitt, who has not beaten the Swiss great in their last 14 meetings.

Whoever wins will next face Davydenko.

Djokovic powered into the quarters with an emphatic 6-1, 6-2, 7-5 win over Poland's unseeded Lukasz Kubot and will meet either France's Jo-Wilfried Tsonga, who he beat in the 2008 final, or Spanish 26th seed Nicolas Almagro.

The Serbian struggled with his form in the opening two rounds, but has moved up a gear and is back with the dominant touch he displayed in the second half of last year.

"I think the first two sets I was very dominant on the court, then he lifted up his level of the game a little bit," he said.

"That's why we had a longer third set. In general, I was very happy with the way I performed today."

Williams and Li join Justine Henin, Nadia Petrova, Maria Kirilenko and Zheng Jie in the last eight.

Williams bounced back from a set down to oust Italian 17th seed Francesca Schiavone 3-6, 6-2, 6-1.

The hard-fought victory under blue skies on Rod Laver Arena keeps her on track for a semi-final with sister Serena, who takes on Australian hope and Australian 13th seed Samantha Stosur later Monday.

Williams is in her 11th Australian Open campaign but is yet to win the singles crown, in stark contrast to Serena, who is a four-time champion and defending her title.

But the elder Williams is not beating herself up about her comparative lack of success in Melbourne, insisting a major part of her game plan was staying positive.

She said she could break her Australian drought this year.

"Yeah, I'm ready to go and I feel very good," said Williams, who has won five Wimbledons and two US Open titles.

"Obviously, I'm hitting the ball pretty good, especially against her today. She was really playing well."

She faces Li next after the 16th seed upset Danish fourth seed Caroline Wozniacki 6-4, 6-3 for her best-ever performance at the Australian Open.

Li's victory broke new ground for Chinese tennis with the 27-year-old joining compatriot Zheng Jie in the last eight, the first time two Chinese players have ever reached that stage of a Grand Slam.

She is looking forward to meeting Williams, who she beat in their only previous match at the 2008 Beijing Olympics.

"I know it'll be tough, but you have to play Venus first and then maybe Serena," she said.

"It was a good experience for me, for my tennis," she added on beating Williams in Beijing.

"But I just want to forget, because I play her again. I don't want to think about the last match. I want to look forward."

If Serena gets past Stosur, she will line up against either Belarrussian seventh seed Victoria Azarenka or ninth seeded Russian Vera Zvonareva.