Nadal is chasing a fifth straight title at the event, and each time he has won in Monte Carlo he has gone on to win the French Open. He has won 17 straight on clay since losing to Juan Carlos Ferrero in the second round of the Rome Masters in May 2008.
"I had some tough moments during the match,'' Nadal said. "I played some games well, I had some terrible games... ( I was) up and down during all the match. I have to improve my concentration in the next match. That's the important thing.''
Roger Federer, who lost to Nadal in the last three Monte Carlo finals, also advanced, beating Andreas Seppi of Italy 6-4, 6-4.
Nadal opened up a 4-0 lead over Chela at the Monte Carlo Country Club, but stuttered after that, losing his serve twice and saving five other break points. The top-ranked Spaniard will next face Nicolas Lapentti of Ecuador, who beat two-time Grand Slam champion Marat Safin of Russia 7-6 (6), 2-6, 7-6 (6).
Federer struggled briefly when serving for the match, trailing 40-30. But the second-ranked Swiss player got a reprieve when Seppi's return bounced out and he then clinched the match when another Seppi return sailed long. It was Federer's first match since getting married last weekend.
"I am very happy to have won my first match on clay,'' said Federer, who can equal Pete Sampras' record of 14 major titles if wins the French Open for the first time. "It takes some time to adjust to the surface, the rebounds and the sliding.''
Federer, who married his longtime girlfriend Mirka Vavrinec in a small ceremony in his hometown of Basel on Saturday, said he began his clay-court preparations 10 days ago, and that Seppi was the ideal first test for him.
"I knew there was going to be some long rallies with Seppi. He's very steady off both sides,'' Federer said. "So on a good day he can be really dangerous. I've already played him twice this year, which was kind of good going into this match, knowing what to expect.''
The biggest adjustment, Federer said, is getting used to clay's unpredictable bounce after playing on hard courts.
"We've been playing on hard court now for nine months ... you never see a bad bounce,'' Federer said. "So all of a sudden you're a little bit worried, sometimes hitting half volleys because they can bounce onto your frame.''
Federer saved two break points in the first set but took his first chance on Seppi's serve in the ninth game to move ahead 5-4. He won the opening set with a backhand down the line. The Swiss star broke Seppi in the opening game of the second set with another backhand pass.
Federer has beaten Seppi three times this year and improved to 5-0 overall without dropping a set against the big-serving Italian player. He will next face 13th-seeded Stanislas Wawrinka, his doubles partner at the Beijing Olympics, on Thursday. Wawrinka beat Martin Vassallo Arguello of Argentina 2-6, 7-5, 6-2.
Fifth-seeded Juan Martin Del Potro of Argentina became the highest seeded player to be eliminated when he failed to capitalize on a good start and lost to wild card Ivan Ljubicic 4-6, 6-1, 6-4.
Seventh-seeded Fernando Verdasco of Spain, No. 8 Nikolay Davydenko of Russia, No. 12 David Nalbandian of Argentina and Simone Bolelli of Italy also advanced. Verdasco beat Philipp Kohlschreiber of Germany 6-3, 6-4; Daydenko defeated Ivo Karlovic of Croatia 6-4, 6-3; Nalbandian beat Marcel Granollers of Spain 4-6, 6-3, 6-1; and Bolelli beat Janko Tipsarevic of Serbia 7-5, 6-3.
Kohlschreiber and Bolelli advance at Monte Carlo
Chela advances at Monte Carlo to meet Nadal
