"I'm just happy to be waking up in the morning and not feeling like an old man," he said. "I have confidence in my movement and confidence in my body."
Also into the fourth round is 119th-ranked Frenchman Stephane Robert, who began the Australian Open as a loser, but will finish it as the winner of at least $135,000.
After failing in his initial attempt to win a place in the 128-man singles draw through the qualifying tournament, Robert grabbed a spot as a lucky loser when Philipp Kohlschreiber withdrew on Monday with injury. Robert then began an extraordinary run that yesterday took him into the fourth round of the Open, the group of 16, and guaranteed him the biggest pay day of his long, but less-than-stellar, career. The Frenchman beat another lucky loser, Slovakia's Martin Klizan, 6-0 7-6 (7-2) 6-4.
Even though winning grand slam tennis matches is something of a novelty for Robert, he has shown flashes of ability before this week. As a qualifier at the 2011 French Open, he beat sixth seed Tomas Berdych in five sets in the first round.
This is Robert's fourth Australian Open and his 10th grand slam appearance. He'd won only four grand slam singles matches in his previous nine and had reached only one ATP Tour level final - which he lost. But in the first month of the new season, Robert, 33, has already made 2014 his best of his 13 years on tour.
"I have played some good matches, but it is difficult to win one, two or three together," Robert said. "This has been a very good start for the year. Maybe it's a good sign." His form at this year's championship has been matched by his French compatriots, eight of whom made the third round, equalling a record in open tennis set at Roland Garros in 1971.
Meanwhile Maria Sharapova concedes she needs to improve to win the Australian Open despite powering into the second week with a 6-1 7-6 (8-6) win over France's Alize Cornet. The Russian third seed's devastating groundstrokes, particularly her inside-out forehand and cross-court backhand, delivered 35 winners to crush Cornet as if she was first-round fodder rather than the 25th seed.
While Sharapova dominated regular play and was able to break Cornet at will, she was broken four times herself and knows she needs to address her service shortcomings.
Again, too, Sharapova struggled to close out. She took 50 minutes between her first and last match points against her last opponent and needed almost 30 minutes to finish off Cornet - she missed a match point with a wayward backhand on the Frenchwoman's serve and then got broken twice while trying to serve for the match.
"I definitely need to step it up. It always gets tougher from here," she said."I can take a few positives from this match, one being I was able to win it not playing my best tennis. After the last match I'm just happy to get through this one and have another day to recover."
Sharapova set up an intriguing fourth-round encounter with 20th seed Dominika Cibulkova, who was ruthless in her 6-1 6-0 demolition of injury-hampered Spanish 16th seed Carla Suarez Navarro. The Slovakian hit 20 winners, has not dropped a set at the Open in three matches and has now repeated her best performance at Melbourne Park. Cibulkova has beaten Sharapova twice in their past three outings.
Outside Open hopes Jelena Jankovic, Simona Halep and Sloane Stephens also progressed to the last 16 as has new Spanish prospect Garbine Muguruza. She ensured former world No.1 Caroline Wozniacki will have to wait until at least the French Open to claim an elusive first Grand Slam title after being beaten 4-6, 7-5, 6-3 by Muguruza in the third round.
Wozniacki, criticised for finishing No. 1 at the end of the 2011 and 2012 seasons without winning a major, had five break points in the second set without converting any of them. Her Spanish rival, meanwhile, converted one of only two chances in the set.
Muguruza, compared frequently with former No. 1-ranked Ana Ivanovic because of her looks and fist-pumping after winning points, won her first WTA tournament two weeks ago at Hobart. Australia's last hope, free-swinging Casey Dellacqua is chasing a $300,000 cash bonanza and maiden grand slam quarter-final berth at the Australian Open. Dellacqua takes on classy Canadian teenager Eugenie Bouchard in the fourth round today.
- AAP