39-year-old Federer, level with Rafael Nadal on 20 Grand Slam singles titles, saw off Uzbek Istomin 6-2, 6-4, 6-3
Naomi Osaka announced she was withdrawing from the French Open on Monday after she was threatened with disqualification for boycotting media duties, while on court, Roger Federer, Serena Williams and Iga Swiatek all reached the second round.
Japanese star Osaka, a four-time Grand Slam champion, said before the tournament that she would not attend press conferences to protect her mental health, saying the traditional post-match inquests are like "kicking people when they're down".
She refused to speak to the media after her first-round victory on Sunday.
The organisers of the four major tournaments -- the Australian, French and US Opens as well as Wimbledon -- responded by fining the world number two $15,000 and threatening her with further sanctions, including defaulting her from Roland Garros.
But the 23-year-old said she has suffered from depression since winning her first Slam in the infamous US Open final three years ago against Serena Williams, and pulled out of the event.
Federer impresses on return
On Court Philippe Chatrier, Federer kicked off only his second French Open campaign in six years with an impressive dismissal of Denis Istomin.
The 39-year-old Federer, level with Rafael Nadal on 20 Grand Slam singles titles, saw off Uzbek Istomin 6-2, 6-4, 6-3.
Federer arrived at Roland Garros having played only three matches since his Australian Open semi-final loss to Novak Djokovic last year, before the Covid-19 pandemic hit.
The Swiss great lost to Pablo Andujar in his first clay-court outing of the season earlier this month in Geneva, but struck 48 winners as he raced to victory over Istomin.
He had been keen to play down any thoughts that he can add to his 2009 Roland Garros title in the run-up to the tournament, but was more positive after his win.
"For me coming back after many months or over a year of rehab, the light at the end of the tunnel or the measuring stick was always can I come back to a good level against good players," said Federer.
"I hope Wimbledon is going to be that place. Maybe there's going to be even something here in Paris. We'll see."
He will next face 2014 US Open winner Marin Cilic.
Serena, Swiatek through
Later on Monday, Serena Williams survived a brief scare against Romania's Irina-Camelia Begu to win 7-6 (8/6), 6-2 in the first ever official French Open night match.
The 39-year-old, still one behind Margaret Court's all-time record of 24 Grand Slam singles titles, saved two set points in the first-set tie-break but dominated from then on.
"It wasn't easy in that first set. I was up and I felt like I had some opportunities," said Williams, who will next face Begu's compatriot Mihaela Buzarnescu.
Serena Williams won the first scheduled night session in French Open history, overcoming two set points to beat Irina-Camelia Begu 7-6 (6), 6-2.https://t.co/5hMmBXQoLN— Los Angeles Times (@latimes) May 31, 2021
The match under the lights on Court Philippe Chatrier was played behind closed doors due to a 9pm curfew imposed by the French government due to Covid-19.
Defending champion Swiatek, celebrating her 20th birthday, saw off her good friend Kaja Juvan 6-0, 7-5 on Court Philippe Chatrier.
Swiatek, who became the first Grand Slam singles title winner from Poland last October, hit 22 winners in an impressive opening to her bid for a second straight Roland Garros triumph.
"I tried to put it behind me (being defending champion) and kind of use it in a positive way because I just know that I'm feeling good here," said the eighth seed.
Medvedev ends miserable run
Daniil Medvedev, who had lost in the first round in all of his four previous appearances in the tournament, put his poor clay-court form behind him by beating the dangerous Alexander Bublik 6-3, 6-3, 7-5.
The two-time Grand Slam runner-up was too strong for Kazakh Bublik, setting up a second-round tie against US player Tommy Paul.
"It was a good match and I've been training really well," said second seed Medvedev.
The Russian is bidding to take advantage of being in the opposite half of the draw to 13-time champion Nadal, Djokovic and Federer, while fourth seed Dominic Thiem was knocked out on Sunday.
Elsewhere, sixth seed Bianca Andreescu was dumped out after losing a marathon first-round match with Slovenia's world number 85 Tamara Zidansek 6-7 (1/7), 7-6 (7/2), 9-7.
Fourth seed Sofia Kenin, last year's losing finalist, did battle through, though, edging out 2017 champion Jelena Ostapenko 6-4, 4-6, 6-3.