The five-time champion was not troubled on Court Philippe Chatrier, and the win kept him on course to equal Bjorn Borg's record of six titles on the Parisian clay.
"I have improved since the tournament started," said Nadal, who was pushed to five sets in the first round. "I'm able to play better and I'm going to continue on this path."
Novak Djokovic also had a successful day, even though he wasn't scheduled to play. The second-seeded Serb reached the semifinals of the tournament -- where he could meet Roger Federer -- when quarterfinal opponent Fabio Fognini withdrew because of injury.
"Walkover from Fognini. Bad luck for him, hope he recovers fast. Today i get to enjoy Paris in a different way :-)" Djokovic wrote on Twitter.
Nadal won four straight titles at the French Open before losing to Robin Soderling in the fourth round in 2009. He will face Soderling in the quarterfinals this year after the fifth-seeded Swede defeated Gilles Simon of France 6-2, 6-3, 7-6 (5).
"For me it will be a tough match," Nadal said minutes before Soderling completed his victory. "He's played two finals here at Roland Garros, so he knows what this means. He's got to play his best tennis."
In an on-court interview after he eliminated Simon, Soderling was told that some people -- including, as it happens, Nadal himself -- are saying the five-time champion isn't at his best.
That drew a comment of "I hope not," and an accompanying chortle from Soderling.
"No, seriously, he's a great player. I think everybody knows what he can do. He won here so many times," continued the Swede, who lost to Federer in the 2009 French Open final. "Every match is different. It doesn't matter how you got to the quarters, as long as you're there."
Federer won the 2009 Open to complete a career Grand Slam, but Nadal returned to win his fifth title in 2010.
Djokovic, who will not be credited with a victory because Fognini withdrew, is after his own records.
If he wins his semifinal match, he would equal John McEnroe's Open era record of 42-0 for the best start to a tennis season and clinch the No. 1 ranking. With three more victories, the second-seeded Serb will match the record of 46 straight wins set by Guillermo Vilas in 1977.
The two-time Australian Open champion has never won the title at Roland Garros, but he beat Nadal in two clay-court finals leading up to the French Open.
Fognini, who injured a muscle in his left leg while beating Albert Montanes on Sunday, announced Monday that he would not be able to play Djokovic, who is 41-0 in 2011 and has won 43 straight matches overall.
"It's better for him," Nadal said of Djokovic's advancement. "He is going to really rest ahead of his semifinal."
"Now I need to recover and at some point I'll stop losing against this Swiss," said Monfils, who has lost five of his six matches against Federer.
"He's in great shape," Monfils said about Federer, "and he hasn't got anything to prove to anyone."
"I wouldn't have believed it," the 31-year-old Chela said,
"if you had told me, seven years later, I would still be here."
Information from The Associated Press was used in this report.