Rafael Nadal wore down an early challenge from French seed Gilles Simon to steam into the fourth round of the Australian Open.

The Spanish second seed fought off six first set points to seal a 7-5, 6-2, 6-3 win on his fifth match point in two hours 26 minutes.

He was tested early by the 28th-seed Simon but finished too strong and fought his way through to a fourth round clash against Austrian Stefan Koubek or Frenchman Paul-Henri Mathieu.

"He started very aggressively and I made some mistakes," Nadal said. "I had some very difficult moments, particularly serving at 5-4 down in the first set. My serve was very important today and I had to serve two aces in that game to hold him out."

Nikolay Davydenko, the fourth seed, had a more comfortable 6-3 6-2 6-3 win over Frenchman Marc Gicquel despite suffering a knee injury that required treatment after a fall.

Davydenko will next meet compatriot Mikhail Youzhny, who had a comfortable 6-2 6-4 6-2 win over Ivo Karlovic.

And France's Jo-Wilfried Tsonga, first round conqueror of Andy Murray, continued his good form with a 6-3 6-4 6-2 defeat of Guillermo Garcia-Lopez.

Nadal has the possibility of claiming the world number one ranking off Roger Federer at this year's Australian Open. But the major obstacle in Nadal's path to the final appears to be sixth seeded American Andy Roddick, who he is due to face in the quarter-finals.

The win was in contrast to the triple French Open champion's ruthless straight sets demolition of Frenchman Florent Serra on Wednesday as he spent more than an hour longer on court against Simon.

Simon squandered six set points after dominating the opening set, failing to handle the pressure as Nadal broke back in the ninth game after losing his service in the second game.

During the sixth game of the opening set Nadal was give a time violation warning while serving. The Frenchman's forehand, which had been rock solid earlier in the set, broke down and the world number two powered back with two service breaks to take the set on his third set point.

Simon's confidence dipped after the setback and he was broken in the first game of the second set when his double-handed backhand skewed wide. He came under pressure in his next service game and was broken again at the third opportunity with Nadal seizing control of the match.

Nadal's decisive break came on Simon's service in the seventh game from two volley errors from the Frenchman. The Spaniard was held up in his march to victory and needed five match points to see him home.