A troubled and at times tormented Rafael Nadal [Images] stumbled through to the French Open fourth round in Paris on Saturday looking anything but the player who is deemed to be invincible on clay.

Frenchman Paul-Henri Mathieu gave the defending champion a nasty 20th birthday fright before the Spaniard prevailed 5-7, 6-4, 6-4, 6-4 on a rowdy Roland Garros centre court.

Mathieu was given little hope before the match but fed off the enthusiasm of home fans in the vertiginous 15,000-capacity arena, leaving Nadal looking clumsy and rattled in a match whose four sets lasted seven minutes shy of five hours.

The 29th seed became the first man to take a set off Nadal at this year's claycourt Grand Slam when the muscular Mallorcan erred with a forehand at 5-6. The first set alone lasted 93 minutes.

Mathieu's varied trajectory and angles troubled Nadal throughout, with his flat double-handed backhand often surprising the Spaniard who had not lost for 55 matches on clay.

Nadal dug in to take the next two sets but looked distinctly unhappy in the third set, first angrily arguing with the umpire over a line call and then calling a medical timeout mid-game after pointing anxiously to his throat.

With both players' socks soaked orange with clay dust Mathieu's will finally broke in the fourth set when he followed a double-fault with three forehand errors to lose serve at 4-4 and then flayed a backhand out on Nadal's first match point.

The fourth round is unlikely to be any easier for Nadal. There he faces Australian Lleyton Hewitt [Images] who beat Slovakian Dominik Hrbaty 7-6, 6-2, 6-2 in a display the former world number one described as one of his best on clay.

"My ball striking was great today. Right from the word go, I served as well as I've probably ever served, especially on clay," said Hewitt who is playing despite an inflamed ankle.

Belgian rivals Justine Henin-Hardenne and Kim Clijsters [Images], together with former world number one Martina Hingis [Images] bulldozed their way into the fourth round with emphatic wins.

DEMENTIEVA UPSET

Israeli Shahar Peer upset Russian sixth seed Elena Dementieva 6-4, 7-5 and will become the first Israeli woman to reach the quarter-finals of a Grand Slam singles event if she beats Hingis in the last 16.

Defending champion Henin-Hardenne bristled with aggression in a 6-4, 6-0 victory over Tathiana Garbin to avenge her defeat by the Italian in a second round shock two years ago.

"In the first set, I have to say I thought a little bit about what happened two years ago," Henin-Hardenne said. "I just tried to change the way I was playing and be a little bit more aggressive."

She will face 2004 champion Anastasia Myskina [Images] in the fourth round.

Clijsters gave a belligerent display against Spaniard Anabel Medina Garrigues and eventually her greater power brought her a 6-3, 6-4 victory.

Hingis demolished Ivana Lisjak of Croatia 6-1, 6-1 to continue her impressive return after a three-year break from the game. The Swiss, who has never won the claycourt Grand Slam, has dropped only 10 games in her three matches so far.

"There's really no need to stay out there longer than you have to," said the 25-year-old, who reached the quarter-finals of the Australian Open in January.

Spaniard Ruben Ramirez Hidalgo, a 28-year-old who had never won a Grand Slam match before the tournament, made it three wins by upsetting compatriot David Ferrer, the 15th seed, 7-6, 7-5, 6-4.

Serbian 19-year-old Novak Djokovic reached his first Grand Slam fourth round with a 7-5, 6-1, 7-6 upset win over German Tommy Haas.

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