Four-time Grand Slam champion Alcaraz struck 31 winners in a 6-3, 6-4, 6-2 victory over Italian qualifier Giulio Zeppieri and will face Hungary’s Fabian Marozsan in round two.
Alcaraz is now on an eight-match winning streak at the French Open and also took Olympic silver at Roland Garros last year, losing the final to Novak Djokovic.
“The first round is never easy, and coming here as a champion is even more difficult,” said the Spaniard, who has won both the Monte Carlo Masters and Italian Open titles on clay this year. “But I started well, found my rhythm, and I’m happy with my start.”
Alcaraz beat Sinner in straight sets in the Rome final just over a week ago as the Italian returned from a three-month doping ban.
Two-time reigning Australian Open champion Sinner saw off home hope Arthur Rinderknech 6-4, 6-3, 7-5 despite a brief third-set wobble in the night session on Court Philippe Chatrier.
It was the first of two successive French opponents for Sinner, who will meet the retiring Richard Gasquet in the second round after the 38-year-old extended his career with a 6-2, 2-6, 6-3, 6-0 win over wildcard Terence Atmane in his 22nd and final Roland Garros.
“I know you’re going to support him (Gasquet), it’s OK, I know that,” Sinner told the crowd, who earlier greeted his arrival on court with loud cheers. “I’m just happy to share a court with him.”
The 75th-ranked Rinderknech fought hard to the delight of the home fans and led 4-0 in the third set.
But he failed to serve out the set at 5-3 ahead and Sinner roared back to secure a straight-sets success with a run of five successive games.
Taylor Fritz of the USA became the first high-profile casualty in the men’s draw as the fourth seed lost 7-5, 3-6, 6-3, 6-1 to German Daniel Altmaier.
Norwegian seventh seed Casper Ruud, a two-time French Open runner-up, got his bid for a first Grand Slam title under way with a 6-3, 6-4, 6-2 win over veteran Spanish qualifier Albert Ramos-Vinolas.
Greek star Stefanos Tsitsipas, the losing finalist in 2021, beat Tomas Martin Etcheverry of Argentina 7-5, 6-3, 6-4.
Two-time quarter-finalist Holger Rune of Denmark also progressed, recovering from losing a first-set tie-break to defeat Roberto Bautista Agut in four sets, as did French number one Arthur Fils.
Swiatek entered the tournament on a near year-long trophy drought but showed signs of form in a 6-3, 6-3 victory over Slovakia’s Rebecca Sramkova.
Her struggles since the last of her four French Open titles have been well documented, but she broke her 42nd-ranked opponent four times in a strong display.
The five-time Grand Slam champion’s remarkable win-loss record in the tournament now stands at 36-2.
“I knew I needed to stay proactive and try to use my weapons. I’m happy with my performance and it was a solid match,” said Swiatek, who also beat Sramkova in the second round of this year’s Australian Open.
Swiatek, who has dropped to fifth in the world rankings, will next face former US Open champion Emma Raducanu after the Briton defeated China’s Wang Xinyu 7-5, 4-6, 6-3.
Raducanu is playing at the French Open for the first time since a second-round exit on her debut in 2022.
Four-time Grand Slam winner Naomi Osaka, who had a match point against Swiatek in the second round at Roland Garros a year ago, was knocked out by Spanish 10th seed Paula Badosa in a tense three-set battle.
Badosa, an Australian Open semi-finalist earlier this year, fought back from a set down to win 6-7 (1/7), 6-1, 6-4.
Osaka has still never got past the third round at Roland Garros.
Former Wimbledon winner Elena Rybakina battled past Argentinian qualifier Julia Riera 6-1, 4-6, 6-4, two days after lifting her first WTA title since April 2024 in Strasbourg.
American ninth seed Emma Navarro suffered an embarrassing 6-0, 6-1 loss to Spanish world number 68 Jessica Bouzas Maneiro in just 57 minutes, only winning a game when her opponent double-faulted to gift her a break when serving for a double-bagel victory.
But her compatriot Madison Keys, the reigning Australian Open champion, had no such problems, swatting aside Daria Saville 6-2, 6-1. (AFP)