Courts were covered as persistent light rain fell, which prompted organisers to announce that play would start at 1000 GMT (6 AM ET) instead of 0900. Forecasters say rain will be a constant problem during the day.
The world No.1 from Spain, who takes on American Robby Ginepri in the first round, has a possible second-round meeting with local favourite Paul-Henri Mathieu and organisers surely want the showdown to be held on the main Philippe Chatrier court.
They said that Nadal usually plays one match on Lenglen before staying on Chatrier for the remainder of the tournament.
Maria Sharapova, the 2012 champion seeded seventh this year, opens proceedings on Chatrier against fellow Russian Ksenia Pervak before Novak Djokovic, who has never won the French Open, plays Portuguese Joao Sousa.
On Court Two, Frenchman Nicolas Mahut is up against Kazakhstan's Mikhail Kukushkin knowing a win would send him to a second-round meeting with American John Isner - the man with whom he played the longest match in tennis history at Wimbledon in 2010.
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