Andy Murray won a scrappy contest against Andrey Golubev in four sets to mark his return to the French Open.
The Wimbledon champion began well but got bogged down in heavy conditions and dropped the third set before recovering to win 6-1 6-4 3-6 6-3.
Murray, who missed the tournament last year with back problems, will play Australian Marinko Matosevic or German-Jamaican Dustin Brown in the second round.
Ivo Karlovic won his first French Open match in seven years to send Grigor Dimitrov crashing out in the first round.
Dimitrov has been one of the stars of the season and, after reaching his first grand slam quarter-final in Australia, he had expected a better showing here.
But 6ft 11in Karlovic is always a man players like to avoid and he has been showing rare good form on clay having reached the final in Dusseldorf last week.
His record at Roland Garros leaves something to be desired, Karlovic having won only two matches in Paris in his career and none since 2007.
But his forehand was on fire as well as his serve and he ousted 11th seed Dimitrov 6-4 7-5 7-6 (7/4), clinching victory with his 22nd ace.
Fifth seed David Ferrer made his return to Court Philippe Chatrier a year after reaching his first grand slam final and was very comfortable in a 6-4 6-3 6-1 win over Igor Sijsling.
Twelfth seed Richard Gasquet, who had not played a match since March because of a back injury, eased his way into the tournament with a 6-2 6-1 7-5 victory over Bernard Tomic.
The Australian, who has won just one match since hip surgery, is again being accompanied to tournaments by his father John following the end of his ATP ban.
Tomic Sr was prevented from gaining accreditation at tournaments for a year after being found guilty of assaulting his son's former hitting partner, Thomas Drouet.
The ban expired earlier this month, and Tomic said: "It's good to have him back. It's been one year and it's been difficult for me.”
French favourite Gael Monfils gave the crowd on Chatrier what they wanted with a 6-2 4-6 6-4 6-2 victory over Victor Hanescu but Michael Llodra has made his last appearance at Roland Garros as a singles player.
The 34-year-old, who will retire at the end of the season, lost 6-2 7-6 (7/4) 7-6 (7/3) to 24th seed Fernando Verdasco.
Two seeds exited through injury, Tommy Haas and Nicolas Almagro both quitting mid match, while Lleyton Hewitt was beaten 3-6 6-2 6-1 6-4 by Argentina's Carlos Berlocq.
The second round begins on Wednesday, with Roger Federer following Rafael Nadal out to Suzanne Lenglen for his match against Diego Schwartzman while Novak Djokovic takes on France's Jeremy Chardy on Chatrier.