The previous longest match had taken place in 1998 when Spaniard Alex Corretja beat Argentina's Hernan Gumy in five hours 31 minutes, also at Roland Garros.

Clement, seeded 32nd, fought back from two sets down against his friend in a first round match interrupted by fading light on Monday evening. Santoro, who made only 40 unforced errors throughout the match, finally prevailed on Tuesday.

The first round match equalled the highest number of games played at the French Open since the introduction of tie-breaks in 1973, with 71 games.

"It's an exceptional moment. More than victory, the intensity of the match and the strong emotions out there are what you're looking for when you become a professional tennis player," Santoro said.