PARIS — What was shaping up as a struggle for Novak Djokovic at the French Open suddenly turned into something of a stroll.

Tied at a set apiece with big-hitting 2009 U.S. Open champion Juan Martin del Potro when play was suspended because of darkness a night earlier, Djokovic quickly faced two break points today. He saved those, then broke del Potro in the next game, and that was pretty much that.

“If he serves well, he can beat anybody, really,” Djokovic said. “I went (into) the match a bit more nervous than usual.”

If that’s so, it didn’t really show. Djokovic completed a 6-3, 3-6, 6-3, 6-2 victory in the third round, pushing his 2011 record to 40-0 and stretching his winning streak to 42 matches overall, including two Davis Cup matches in December.

“He was much better than me,” said the 25th-seeded del Potro, a semifinalist in Paris two years ago. “He has everything; everything perfect. He has very good movement. He’s very fast. He’s improved his serve. He’s beating all the players very, very easy, and I’m one more victim of his game.”

Djokovic’s 42-match run is tied for the third-longest by a man in the Open era, which began in 1968; Guillermo Vilas won 46 in a row in 1977. And Djokovic is off to the second-best start to a season, trailing only John McEnroe’s 42-0 in 1984.

As it happens, the 24-year-old Serb ran into McEnroe at Roland Garros today, and they chatted. Asked whether McEnroe was one of his favorite players, Djokovic replied with a smile: “Nothing against his age, but it’s just that I was still quite young when he stopped playing.”

McEnroe said recently he finds Djokovic’s streak more impressive than his own, because of the current depth in men’s tennis, and because it includes a Grand Slam title – at January’s Australian Open, which was played at season’s end in 1984.

Djokovic, who will be in action for a third straight day Sunday when he faces No. 13 Richard Gasquet of France, said a third major championship – and first at the French Open – takes priority over any other possible goal at the moment. If he gets to the final, he’ll take over the No. 1 ranking from Rafael Nadal.

Djokovic is 4-0 this year against Nadal, including wins in two clay-court tournament finals this month, and some have speculated those results chipped away at the Spaniard’s self-belief. Nadal felt much better about himself and his game after reaching the fourth round by beating Croatian qualifier Antonio Veic 6-1, 6-3, 6-0.

“Solutions don’t come from heaven. I mean, you can’t change everything in one day. And you know what? I had not forgotten how to play tennis for a week, but I played better today,” said Nadal, who was pushed to five sets in the first round.

He’s 41-1 in his French Open career and bidding to tie Bjorn Borg’s mark of six titles at the clay-court Grand Slam tournament.

The man Nadal beat for trophy No. 5 in last year’s final, Robin Soderling, also reached the fourth round, as did three-time Grand Slam runner-up Andy Murray, No. 15 Viktor Troicki, No. 18 Gilles Simon, and unseeded Ivan Ljubicic, who eliminated No. 16 Fernando Verdasco 6-3, 7-6 (6), 6-4 and meets Nadal on Monday.

“There is no question that his confidence is shaken,” Ljubicic said about Nadal. “You see him in the locker room. He’s saying it. He’s not hiding it.”

No. 4 Murray got past Michael Berrer of Germany 6-2, 6-3, 6-2 despite badly twisting his right ankle while chasing a drop shot in the second set, then said he wasn’t sure if he could play his next match.

Berrer chastised himself for not taking advantage.

“I should have hurt him when he’s down, but that’s difficult for me. So I was feeling sorry for him,” Berrer said. “I need to be tougher. Like, in Germany, we have a saying that ‘an injured deer has to fall.’ So that was what I should have done today.”

France’s Simon beat No. 10 Mardy Fish 6-3, 6-4, 6-2. That result, plus Vania King’s 6-4, 6-2 loss to No. 9 Petra Kvitova of the Czech Republic, mean there are zero U.S. men or women left in the singles draws as the tournament enters Week 2.

Twenty-eight of the 32 players still around in both fields are from Europe. That includes three Russian women who won today: No. 7 Maria Sharapova, No. 25 Maria Kirilenko and unseeded Ekaterina Makarova.

Also advancing: No. 4 Victoria Azarenka of Belarus, No. 6 Li Na of China, No. 12 Agnieszka Radwanska of Poland, and No. 15 Andrea Petkovic of Germany.

Kirilenko put together a 6-1, 6-1 victory that abruptly ended the surprising run of 114th-ranked Arantxa Rus of the Netherlands, who stunned No. 2 Kim Clijsters in the second round by taking 11 of the last 12 games.

Sharapova also needed a big comeback to win her previous match – she claimed the final 11 games after trailing a 17-year-old wild-card entry – but faced no such trouble in beating Chan Yung-jan of Taiwan 6-2, 6-3.

With the Clijsters out, and the Williams sisters sidelined after health issues, Sharapova’s three major titles give her the same number as the other 15 women still around combined.

“Every day is different, and you face different opponents,” said Sharapova, who would complete a career Grand Slam by winning the French Open. “And you can never be overly confident, because if you are, then I don’t think you push yourself, you motivate yourself enough.”