Federer beat Sonego, who was making his French Open debut, handily on the refurbished Court Philippe Chatrier during the opening day of the tournament. The 20-time Grand Slam champion won in straight sets 6-2, 6-4, 6-4.
Federer, a No. 3 seed in this year's tourney, previously missed the French Open in 2016 due to a back injury. He skipped the event in 2017 and 2018 to prepare for Wimbledon. He won the title in Paris 10 years ago to complete a career Grand Slam.
"I knew I can play very well on clay and I am very happy I did it in straight sets today," Federer said to the crowd after the match. "I missed the French crowd so thanks for the warm welcome today."
In other men's action, No. 16-seeded Marco Cecchinato was eliminated in the first round. A year after upsetting Novak Djokovic in Cecchinato's run to the French Open semifinals, Nicolas Mahut rallied from two sets down to defeat the Italian 2-6, 6-7 (6), 6-4, 6-2, 6-4.
11th-seeded Marin Cilic and sixth-seed Stefanos Tsitsipas each won in straight sets. No. 7 Kei Nishikori defeated Quentin Halys 6-2, 6-3, 6-4 to advance to the second round.