Clijsters and Wozniacki through as Nadal has it easy

Kim Clijsters and Caroline Wozniacki are on course for a quarter-final clash while Roger Federer's rival is forced to withdraw and Mardy Fish cries foul after exit.

Belgium's Kim Clijsters plays a backhand against Stephanie Foretz Gacon of France.

MELBOURNE // Rafael Nadal and Roger Federer continued their march ahead at the Australian Open in contrasting fashions today, and so did Kim Clijsters and Caroline Wozniacki in the women's singles while Mardy Fish, the highest-ranked American was the biggest casualty.

While Nadal, the world No 2, had no problems dispatching Germany's Tommy Haas, Federer was given a free ride into the third round after German Andreas Beck withdrew with injury.

The Swiss, seeded third, was due to play lefthander Beck on Hisense Arena but the 25 year old was forced to pull out with a lower back problem.

Nadal's knee is fine: Nadal, a 10-time grand slam champion, won 6-4, 6-3, 6-4 in 2hr 29min against Haas, a three-time semi-finalist in Melbourne.

The 2009 winner gave a reminder of his past glories with some great shot-making, particularly with his trademark one-handed backhand, and showed no signs of discomfort after an injury scare with the right knee.

"He's [Haas] a fantastic player and he's had a lot of injuries over the last couple of years and it's great to see him back," Nadal said.

Nadal, who again played with his knee heavily bandaged, said he was happy with the knee's progress. "It's much better and I'm happy with how the knee is improving and I played today without any problems," he said.

The women's defending champion, Clijsters needed only 47 minutes to beat Stephanie Foretz Gacon of France 6-0, 6-1, then showed just how much support she has at Rod Laver Arena by getting the crowd to sing 'Happy Birthday' to her younger sister.

The top-ranked Wozniacki seemed to be on the same trajectory, but had to battle to beat Anna Tatishvili of Georgia in the second set, recovering two service breaks and saving a set point en route to a 6-1, 7-6 (4) win.

She needs to reach the quarter-finals to have a chance of retaining the top ranking she held for all but one week in 2011. That is also the stage when she could come across Clijsters.

The No 11-seeded Belgian showed no signs of a hip problem that forced her to retire during a semi-final against Daniela Hantuchova at a warm-up tournament two weeks ago.

She will meet Hantuchova in the next round here, and has a potential rematch of the 2011 Australian Open final with French Open champion Li Na in the fourth round.

Among the upsets, 10th-seeded Francesca Schiavone was eliminated 6-4, 6-3 by fellow Italian Romina Oprandi and Peng Shuai (No 16) lost 6-2, 6-4 to Iveta Benesova of Czech Republic.

Fish says foul: Eighth-ranked Fish became the first top 10 player on the men's side to lose, falling 7-6 (4), 6-3, 7-6 (6) to Colombia's Alejandro Falla. But the American claimed later Falla's frequent stoppages to treat leg cramps was not fair practice.

"I see that guy's called the trainer three, four times, however many times he was out there," Fish said. "It's hot and I'm down two sets to love and I'm looking for anything to sort of gain the momentum a little bit."

"I thought he was having some physical issues. But then in between on every point he was totally fine."

"I'm not feeling great, either. It was three hours and it's pretty hot out. It is what it is."

World No 7 Tomas Berdych triumphed 6-1, 6-0, 7-6 (4) over Olivier Rochus of Belgium, while the 2009 US Open champion Juan Martin del Potro, Feliciano Lopez (No 18) and Kevin Anderson (No 30) all advanced.

Meanwhile Federer said his opponent had told him of the problem in the locker room.

"He said, 'I'm not so good actually. I have a bad back'," Federer told reporters. "It came as a surprise. He said he had a lot painkillers and pain during the last match. I think it happened four, five days ago.

Federer, targeting a fifth Australian Open title at Melbourne Park, will meet either Croatia's Ivo Karlovic or Argentine Carlos Berlocq in the third round.

The withdrawal spared Federer a first match away from Rod Laver Arena since he met Jeff Morrison in the second round in 2004.

More controversy: David Nalbandian was left fuming at the chair umpire after he over-ruled a call and denied him a Hawk-eye challenge towards the end of his marathon 4-6, 6-3, 2-6, 7-6, 10-8 loss to American John Isner.

With Nalbandian holding a break-point at 8-8 in the decider, umpire Kader Nouni over-ruled a first serve by Isner as an ace after it was called a fault.

The Argentine walked up to inspect the mark where the ball had bounced and demanded a challenge, but was denied by Nouni who ruled he had not made it quickly enough.

There is no time set that players are bound by to mount challenges and it is up to the umpire's discretion.

A non-plussed Nalbandian remonstrated with Nouni for some minutes, before he grudgingly returned to the baseline with the score at deuce.

Isner held serve to lead 9-8 and subsequently broke his opponent in the next game to seal the four-hour and 41-minute match.