PARIS - Novak Djokovic and Rafael Nadal, the top two favorites at Roland Garros and the finalists of last year, kicked off their campaign both with straight-set wins on Tuesday.

The 34-year-old Spaniard was forced to save a set point in the third set but held his nerve to defeat Australia's Alexei Popyrin 6-3, 6-2, 7-6 (3).

The Serbian top seed, playing under the light in the night session, eased past Tennys Sandgren of United States 6-2, 6-4, 6-2.

However, Russia's seventh seed Andrey Rublev was shocked by Germany's world No. 42 Jan-Lennard Struff in a thrilling five-set battle. Struff powered to a two-set lead but lost the third and fourth before restoring in the deciding set to pocket the victory 6-3, 7-6 (6), 4-6, 3-6, 6-4 after three hours and 46 minutes.

With the seedings based on the world rankings, four-time reigning champion Nadal, seeded third, was drawn in the same half with Djokovic and Switzerland's giant Roger Federer who came to Paris as the eighth seed.

"I'm here to try my best, and when you are the third seed, you know that you're going to have the chance to be in the same part in the draw with the number one or the number two," said Nadal, who is bidding to win his 21st Grand Slam title, a feat would make him break the tie with Federer to take sole ownership of the all-time record for most Grand Slam men's singles titles.

The King of Clay clinched his 13th Grand Garros title by beating arch-rival Djokovic in a lopsided final 6-0, 6-2, 7-5 last year.

"I have won my first match, something that I'm happy with and I'm focused on the second one. That's it. The other stuff doesn't worry me much now," Nadal said.

Djokovic's opening round match with Sandgren was the first-ever men's night session on Court Philippe-Chatrier as the 2016 champion took a comfortable win.

"It was strange to play under the lights, they were very bright, to be honest," said the 18-time Grand Slam winner.

"Overall from the later stages of the Rome tournament until now, I'm just finding my groove on the court and striking the ball well. Very pleased with the way I am feeling and playing on the court,"

Djokovic is bidding to become the first man in the Open Era to win each of the four Grand Slam titles twice and close the gap with Federer and Nadal on the Grand-Slam win list.

Top-seeded Ashleigh Barty fended off a second-set fightback from Bernarda Pera in women's events, beating the American 6-4, 3-6, 6-2 to progress.

Barty, who skipped the French Open in 2020 due to the COVID-19 pandemic, returned to the clay Grand Slam with good form, winning the title in Stuttgart and reaching the final in Madrid. Striving for her second Roland Garros title after winning in 2019, Barty will face off against Magda Linette of Poland in the next round.

Fifth seed Elina Svitolina bounced back from a 5-2 deficit in the second set to defeat teenage wildcard Oceane Babel 6-2, 7-5 in earlier action.

But it was an unfortunate story for last year's semifinalist Petra Kvitova as the Czech 11th seed was forced to withdraw from the tournament after picking up an ankle injury during her "post-match press requirements."

"It is with great disappointment that I announce my withdrawal from Roland Garros. During my post-match press requirements on Sunday I fell and hurt my ankle," the two-time Wimbledon champion wrote on Twitter. "Unfortunately, after an MRI and much discussion with my team, I have made the tough decision that it would be unwise to play on it."

The world No 12 came through her opening round encounter against Greetje Minnen 7-6(3), 6-7(5), 6-1 to set up a second-round meeting with Elena Vesnina.