Wawrinka, who lost to Nadal in last year's final, showed little positive sign of coming back from his knee injury, as he lost to Spain's Guillermo Garcia-Lopez 6-2, 3-6, 4-6, 7-6 (5), 6-3.

However, the Swiss shrugged off any connection between the tough loss and his knee plague.

"It's completely unconnected. That's the positive of today," he said.

Novak Djokovic swept Grand Slam titles two years ago in Paris, while competing in this year's tournament as No 20 seed, his lowest Grand Slam seeding since the 2006 U.S. Open after an elbow injury forced him to be sidelined from many tournaments last year.

The Serbian saw off Brazil's Rogerio Dutra Silva 6-3, 6-4, 6-4, joining seeded players Dominic Thiem, Diego Schwartzman and Sam Querrey in the second round.

"It has been difficult to face the most challenging injury that I have ever had," recalled Djokovic.

"It's been a long 12 months behind me, but I'm starting to play better. In the past couple of weeks, I feel like playing pain free, not thinking about the elbow," he added.

Second-seeded Caroline Wozniacki withstood challenge from Danielle Collins of the United States to move past the women's singles first round 7-6 (2), 6-1.

Women's prominent names Petra Kvitova and Karolina Pliskova also marched on, while former world No 1 Victoria Azarenka fell short at 7-5, 7-5 against Katerina Siniakova.

China's Zhang Shuai, Peng Shuai and Duan Yingying will kick off their campaign at the 2018 French Open on Tuesday.