To get an assessment of how much better Rafael Nadal and Roger Federer are than most of the competition in men's tennis, look no further than Marcos Daniel.

At the Australian Open yesterday, Daniel was on the other side of the net from Nadal, who is attempting to win his fourth major title in a row, the "Rafa Slam." Daniel saw, ever so briefly, why the top-seeded Nadal is among the best ever in the game.

Only briefly, because the Brazilian's left knee gave out, forcing him to retire from the first-round match while already trailing 0-6, 0-5.

"If you see all the top five guys, they improve so much," said Daniel, who has also lost to Federer. "They are one step forward, faster than the others, they hit the ball harder than the others, they can stay very focused for four hours, different than the others. Imagine Federer and Nadal, they are the same."

Nadal will next play American qualifier Ryan Sweeting, who beat Daniel Gimeno 6-4, 6-4, 6-1.

Another of those top five that Daniel mentioned was Andy Murray, the 2010 finalist who also advanced when Karol Beck retired with a shoulder injury in the third set of their first-round match. The fifth-seeded Murray, who was leading 6-3, 6-1, 4-2, was the only man to beat Nadal in a grand slam tournament last year, the quarterfinals at Melbourne Park.

Fourth-seeded Robin Soderling had to go the distance but was rarely challenged, completing a 6-4, 6-2, 6-2 win over Potito Starace of Italy.

David Nalbandian of Argentina beat former No. 1 Lleyton Hewitt of Australia 3-6, 6-4, 3-6, 7-6 (1), 9-7 in a feature-length replay of their 2002 Wimbledon final won by the Australian.

Going into yesterday's match, Hewitt led the series 3-2 but had not beaten Nalbandian since a controversial 2005 Australian Open quarterfinal in which the pair bumped into each other purposely on a changeover. The video clips of that altercation featured prominently on television promotions of the night Rod Laver Arena match.

After the 2005 match, won in five sets by Hewitt, Nalbandian said he was "not a gentleman'" and "nobody is friends" with the Australian.

Hewitt said Nalbandian was "not the cleanest guy."

There appeared to be no such animosity yesterday, with both players mostly on their best behavior.

They shook hands and nodded at each other at the end of the 4-hour, 48-minute match.

Hewitt's biggest stumbling block was his inability to convert break-point chances: just seven of 30. Nalbandian was six of 12, but only two of eight in the final set.

Nalbandian, who was cramping at the end of the marathon match, saved two match points on his serve before finishing it at 1:10am local time today with a perfect lob on his first match point.

"It doesn't matter that we are tired, we keep fighting," Nalbandian said. "I can't talk I am so tired."

Elsewhere, No. 15 Marin Cilic of Croatia beat American qualifier Donald Young 6-3, 6-2, 6-1 to advance, along with No. 7 David Ferrer, No. 10 Mikhail Youzhny, No. 11 Jurgen Melzer and No. 20 John Isner.

Jo-Wilfried Tsonga, who lost in the final here to Novak Djokovic in 2008, came back from two sets down to beat Philipp Petzschner of Germany 4-6, 2-6, 6-2, 6-3, 6-4. Andreas Seppi of Italy beat Arnaud Clement of France 3-6, 2-6, 7-5, 6-3, 6-2 in another late match.

On the women's side, US Open champion Kim Clijsters did nothing to dent her growing status as tournament favorite by routing former No. 1 Dinara Safina 6-0, 6-0. The US Open champion never allowed the 2009 Australian Open finalist to get into the match, placing pinpoint forehands to all areas of the court. When Safina did have an opportunity to return, her many unforced errors gave away the point to Clijsters.

No. 2-ranked Vera Zvonareva began her bid to reach a third consecutive grand slam final with a 6-2, 6-1 win over Sybille Bammer.

Ana Ivanovic, the 2007 French Open champion and 2008 Australian Open finalist, slumped to her worst result in seven years at Melbourne when she lost 6-3, 4-6, 8-10 to Russia's Ekaterina Makarova.

Also advancing were French Open finalist Sam Stosur, the fifth-seeded Australian who beat American wildcard entry Lauren Davis 6-1, 6-1; No. 12 Agnieszka Radwanska, who took six of the last seven games after a medical timeout in the third set to hold off Japanese veteran Kimiko Date Krumm 6-4, 4-6, 7-5; No. 7 Jelena Jankovic; No. 10 Shahar Peer and No. 13 Nadia Petrova.