Former champion Amelie Mauresmo suffered her earliest Australian Open defeat since 2000 when she was upended 3-6 6-4 6-4 by unseeded Australian Casey Dellacqua in the third round.

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The Frenchwoman, who slipped down the rankings to 18th at the end of last year, led by a break of serve in the final set but Dellacqua hit back to clinch the biggest victory of her career.

Mauresmo double-faulted 10 times but still had her chances, breaking for 4-3 in the final set only to lose the last three games.

World number 78 Dellacqua, who had only ever won one Grand Slam match before this year, next plays third seed Jelena Jankovic.

Jankovic shrugged off fatigue and nagging injuries to earn a 6-2 4-6 6-1 victory over Virginie Razzano of France.

The Serb had struggled through her opening two matches, saving three match points against Tamira Paszek in the first round, and the clash with Razzano was no different.

After racing into a 3-0 lead, Jankovic struggled, consistently forced to break serve to stay in the contest when her own service game was placed under pressure.

The 22-year-old, hampered by a shoulder injury and fatigue during her second-round match, lost the second set but ran away with the third and clinched victory on her second match point.

Justine Henin, the 2004 champion at Melbourne Park, advanced by beating tricky Italian Francesca Schiavone 7-5 6-4.

Henin had problems with her serve in a match characterised by exploiting angles and opening up the court rather than power, but was able to break Schiavone when she needed to.

The 25-year-old Belgian had to battle back from two break points when serving for the match and secured victory when Schiavone's desperate return from a smash went wide.

Henin has now won 31 consecutive matches since losing in last year's Wimbledon semi-finals to Marion Bartoli.

The top seed next meets Taiwan's Hsieh Su-wei, who had never won a Grand Slam match prior to this tournament, after Hsieh beat France's Aravane Rezai 6-2 6-7 6-5.

World number 158 Hsieh, who plays double-handed on both sides, has now won six matches to get to the fourth round, having come through the qualifying competition.

While Rezai tried to out-power Hsieh, the Taiwanese mixed up the pace, even resorting to moon-ball tactics in an effort both to upset the rhythm of the Frenchwoman and to recover from a series of long rallies.

Defending champion Serena Williams, meanwhile, booked her place in the fourth round with a routine 6-3 6-4 win over Victoria Azarenka of Belarus.

The seventh-seeded American struggled for fluency throughout the match but was always too strong for the 26th seed, sealing a convincing victory in 72 minutes.

Williams next plays 12th seed Nicole Vaidisova for a place in the quarter-finals after the Czech ousted Japan's Ai Sugiyama.

Elena Vesnina but up a spirited battle but in the end the former Wimbledon and US Open champion Maria Sharapova had too much power and too much nous for her compatriot.

Fifty ranking places separate world number five Sharapova and Russian compatriot Vesnina but the gulf in class was gaping.

Vesnina held on in the opening set before folding in the second, slumping 6-3 6-0. Next up for Sharapova, runner-up at Melbourne Park 12 months ago, is another blonde Russian baseliner, Elena Dementieva.

The 11th seed rolled over Israel's Shahar Peer 6-2 6-0.

Eurosport