Del Potro latest to fall to unbeaten Djokovic at French Open

The Serb reaches 40-0 for 2011 after beating Juan Martin del Potro 6-3, 3-6, 6-3, 6-2 in the third-round of the French Open.

Novak Djokovic clenches his fist in celebration after beating Juan Martin del Potro at Roland Garros.

PARIS // Novak Djokovic extended his perfect start to the season at the French Open, beating Juan Martin del Potro 6-3, 3-6, 6-3, 6-2 for his 40th straight victory this year.

Djokovic has not lost in 42 matches dating to last year's Davis Cup final. He and Del Potro returned to Court Suzanne Lenglen today after splitting the first two sets last night before the match was suspended because of fading light.

The world No 2 had no problems against Del Potro, the 2009 US Open champion, once play resumed. He had 41 winners to Del Potro's 22 and had four of his five breaks in the final two sets.

Rafael Nadal also appeared to put his struggles behind him, advancing to the fourth round with a 6-1, 6-3, 6-0 win over the Croatian qualifier Antonio Veic. the Australian Open runners-up Andy Murray and Li Na also advanced.

Later today, three-time grand slam champion Maria Sharapova was scheduled to be on court.

Djokovic's 40-0 start to 2011 is the second-best opening streak in the Open era, which started in 1968. The two-time grand slam champion's overall winning streak of 42 trails only to the record of 46 set by Guillermo Vilas in 1977.

Djokovic entered the French Open after beating Nadal in two clay court finals, making him a favourite for his first French Open title. The Serb will be guaranteed to take over the No 1 ranking if he makes the final.

In the next round, Djokovic will face the No 13 Richard Gasquet of France.

Nadal, who needed five sets to win his opening match at Roland Garros, had only 18 unforced errors and managed to break his opponent nine times.

The five-time French Open champion has been dominant at Roland Garros since his debut in 2005, when he won the first of four straight titles. His only loss at the clay court grand slam came in 2009, when he was defeated by Robin Soderling in the fourth round, giving him a 41-1 record at the tournament.

But Nadal started off slowly this year, needing five sets to beat John Isner. In the second-round, Nadal looked shaky in defeating Pablo Andujar 7-5, 6-3, 7-6 (4).

"I did a few things much better than the previous days. Happy for that," Nadal said. "Just the beginning of the second, for moments of the second set, I had a few more mistakes. But for the rest of the match, I think I started to have better control of the ball."

Murray moved into the next round despite twisting his right ankle in the second set against Michael Berrer. The No 4 seed called for a trainer and had his ankle taped before returning to the court. He broke his German opponent on the next point and went on to a 6-2, 6-3, 6-2 victory.

Berrer said he failed to take advantage of the situation.

"That was a very big chance. I think a chance like this you get maybe once in your life," Berrer said. "I should have hurt him when he's down, but that's difficult for me."

Murray will next face Victor Troicki of Serbia, who beat the No 21 Alexandr Dolgopolov of Ukraine 6-4, 3-6, 6-3, 6-4.

Juan Ignacio Chela of Argentina reached the fourth round by defeating Lukas Rosol of the Czech Republic 6-2, 6-4, 3-6, 7-6 (5).

In the women's draw, the No 6 seed Li, who this year became the first Chinese player to get to the final at a major tournament, defeated Sorana Cirstea of Romania 6-2, 6-2 and will next play the No 9 seed Petra Kvitova. Li has made at least the quarter-finals at the other three grand slam tournaments, but she has never progressed past the fourth round at Roland Garros.

Kvitova defeated Vania King of the United States 6-4, 6-2, while Ekaterina Makarova of Russia eliminated No 16 Kaia Kanepi of Estonia 6-4, 7-5. Fourth-seeded Victoria Azarenka of Belarus also advanced, beating No 30 Roberta Vinci of Italy 6-3, 6-2.

"I think I can improve, and I have been improving from match to match, which is important," Azarenka said. "Probably could do things better, but I have time to work on and prepare for the next match."