PARIS — Novak Djokovic extended his perfect start to the season at the French Open on Saturday, 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 on Saturday after splitting the first two sets Friday before the match was suspended because of darkness.
The second-seeded Serb had no problems on Day 2 against Del Potro, the 2009 U.S. Open champion. He had 41 winners to Del Potro's 22 and had four of his five breaks in the final two sets.
"I knew before we played this match that it's going to be a definitely difficult opponent to beat, a player who can equally play well on different surfaces," Djokovic said. "I was managing to control my game a little bit better today than I did yesterday. I think that resulted with the win."
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 Croatian qualifier Antonio Veic. Australian Open runners-up Andy Murray and Li Na also advanced, as did three-time Grand Slam champion Maria Sharapova.
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 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 contender for his first French Open title. The Serb will take over the No. 1 ranking if he makes the final.
"Today he's done much better than me and he took his opportunities and made the match very difficult," Del Potro said. "I had my chance in third set, 2-all, two break points, and I miss it. Against this player, if you don't take your chance, you lose."
In the next round, Djokovic will face No. 13 Richard Gasquet of France, who advanced Friday with a 6-2, 6-3, 3-6, 6-3 victory over Thomaz Bellucci of Brazil.
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 also 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 fourth-seeded Brit 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.
"I just rolled my ankle, and then, obviously, pretty sore for the rest of the match," said Murray, adding that he would decide later if he can play in the next round. "I've just got to wait and see how it pulls up or do all the right things to make sure, give it my best possible shot for the next match."
Murray would play Victor Troicki of Serbia, who beat No. 21 Alexandr Dolgopolov of Ukraine 6-4, 3-6, 6-3, 6-4.
Also, No. 18 Gilles Simon eliminated 10th-seeded Mardy Fish of the United States 6-3, 6-4, 6-2, Juan Ignacio Chela of Argentina defeated Lukas Rosol of the Czech Republic 6-2, 6-4, 3-6, 7-6 (5) and Alejandro Falla of Colombia beat Lukasz Kubot of Poland 6-7 (4), 6-4, 7-5, 6-4.
The seventh-seeded Sharapova moved into the fourth round by overpowering Yung-Jan Chan of Taiwan 6-2, 6-3 on center court.