Federer, who is seeded eighth, won the French Open for the only time in 2009
Roger Federer eased through his French Open return with a straight-set win over Uzbekistan's Denis Istomin.
The 20-time Grand Slam champion had not played at Roland Garros since 2019 and was playing his first match at a major in 16 months after a knee injury.
The 39-year-old Swiss played smoothly and confidently as he won 6-2 6-4 6-3.
Meanwhile, Russian second seed Daniil Medvedev ended his misery at Roland Garros as he beat Alexander Bublik for his first win on the Paris clay.
Medvedev, 25, won 6-3 6-3 7-5 against Kazakhstan's Bublik, ending a run of four successive defeats in round one.
Elsewhere in the men's singles draw on Monday, Croatia's Marin Cilic set up a second-round meeting with Federer following a 7-6 (8-6) 6-1 6-2 win against Frenchman Arthur Rinderknech.
Belgian 13th seed David Goffin was beaten in straight sets by Italian 19-year-old Lorenzo Musetti, the Lyon Open semi-finalist winning 6-0 7-5 7-6 (7-3) to claim his first victory at a Grand Slam.
Norwegian 15th seed Casper Ruud, 22, overcame Benoit Paire 5-7 6-2 6-1 7-6 (7-4), while John Isner won an all-American match against Sam Querrey 7-6 (7-2) 6-3 6-4.
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Federer happy with 'good performance'
Federer was the star attraction in the men's singles on the second day of the clay-court Grand Slam, reintroducing himself to the top level after missing the past three majors.
The Swiss, who turns 40 in August, was playing in a Grand Slam for the first time since the 2020 Australian Open semi-finals, having needed two knee operations during the pandemic.
He returned to the match court at Doha in March, beating British number one Dan Evans in his comeback match before losing to Georgia's Nikoloz Basilashvili a day later.
However, he did not play again until the Geneva Open last month, losing to Spain's Pablo Andujar in his one and only clay-court match in the past two years.
Expectations of a deep run at Roland Garros have been dampened by Federer, who said he is focusing on building up his form and fitness to peak at next month's Wimbledon.
Yet he looked in majestic form in the first match of what is only his second appearance on the Paris clay since 2015.
"I'm very happy. It was a good performance. I just felt overall much clearer, much better than I did in Geneva," said Federer.
Federer wrapped up the first set in 23 minutes, going on to secure victory in one hour and 33 minutes without facing a break point.
As well as converting five of his 13 break points, the Swiss hit 48 winners and won 80% of first-serve points in an impressive all-round performance.
"In a way I like this situation, that I don't know what's next, how my next match will be," said Federer.
"I take it round by round, match by match. I think it's going to help me, with the way I go about it."
Is Medvedev starting to enjoy clay?
Daniil Medvedev reached the 2019 US Open final and the 2021 Australian Open final
Medvedev, a two-time Grand Slam finalist, broke out into a relieved grin after serving out for victory in under two hours.
"I felt I was not playing well in the past here, but this time I feel comfortable," the Russian said.
"I am running well and moving well. I want to keep playing at this level."
Medvedev has rarely concealed his dislike for the red dirt, having earned just 11 of his 179 career wins on the surface going into Roland Garros.
He had earned only one clay-court victory – against Spain's Alejandro Davidovich Fokina in Madrid – this year.
Despite calling it the "worst surface ever" at the recent Italian Open, Medvedev said in his pre-Grand Slam news conference that practice in Paris had been "amazing" and that the conditions helped him play like he does on hard courts.
That showed in a dominant performance against Bublik, where the hotter and faster conditions seemed to suit his game.
Medvedev is seeded second at Roland Garros – one above 13-time champion Rafael Nadal – because the seedings are based on world rankings, meaning the Russian finds himself in the opposite side of the men's draw to Nadal, top seed Novak Djokovic and Federer.
There are no Grand Slam champions in his half following US Open winner Dominic Thiem's defeat on Sunday.
Greek fifth seed Stefanos Tsitsipas and German sixth seed Alexander Zverev – who are both strongly tipped to go far – remain in there after winning their opening matches.
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