PARIS (AFP) - German fifth seed and reigning Wimbledon champion Angelique Kerber was knocked out of tennis' French Open in the first round on Sunday (May 26) by Russian world No. 81 Anastasia Potapova.

Kerber, bidding to complete a career Grand Slam, slumped to a 6-4, 6-2 defeat by the 18-year-old, who was making her Paris debut.

Kerber had come into Roland Garros carrying a right ankle injury which forced her to pull out of the Italian Open and retire from her second-round tie in Madrid.

"I had a lot of confidence and I have to thank my coach for that," said Potapova, who hit 28 winners past her German opponent, who has now lost six times in the French Open first round.

The Russian's first win over a top-10 player gives her a second-round clash against either China's Wang Yafan or Marketa Vondrousova of the Czech Republic.

"She played really good, I tried my best," said Kerber, who was broken six times in the match which brought the curtain up on a rebuilt Court Philippe Chatrier. "I didn't really have great preparation and I was just happy to get on court to play the match.

"I didn't have many expectations coming in."

Later on Sunday, Federer returns to the new-look Roland Garros, admitting he will be an underdog in his attempt to claim a 21st Grand Slam title.

The 37-year-old Swiss star is the headline act on opening day, 10 years after his only triumph in Paris and two decades since his tournament debut.

Federer, who played his last French Open in 2015, preferring to concentrate his powers on Wimbledon, starts against Lorenzo Sonego, the world No. 73 from Italy. The third seed insists that it would be a shock even to him should he manage to prevent either Rafael Nadal from sweeping to a 12th title or Novak Djokovic becoming just the second man to hold all four Slams at the same time twice.

"I feel like I'm playing good tennis, but is it enough against the absolute top guys when it really comes to the crunch? I'm not sure if it's in my racquet," he said.

Stefanos Tsitsipas moved into the second round with a comfortable straight-sets win over German left-hander Maximilian Marterer on Court Philippe Chatrier.

The 20-year-old sixth seed, a semi-finalist at the Australian Open earlier this year, brushed aside the world No. 110 6-2, 6-2, 7-6 (7-4).

The Greek raced into a 2-0 lead and edged a third-set tie-break to see off an opponent who reached the fourth round in Paris last year.

"It was a difficult first match... In the tie-break I managed to play like I did in the first two sets," said Tsitsipas, who was playing on the Roland Garros show court for the first time.

"These are the moments we're practising for and dreaming of, I'm really happy to play here."

Tsitsipas will next face either Indian Prajnesh Gunneswaran or Bolivia's Hugo Dellien as he looks to reach the third round for the first time.

He also defeated Nadal in the Madrid semi-finals before falling to the Spaniard at the same stage in Rome last week.

New court set for unveiling

Second seed Karolina Pliskova closes play on Chatrier against Madison Brengle of the United States. The centrepiece court of Roland Garros has been demolished and 90 per cent rebuilt since 2018 as part of the €350 million (S$540 million) refurbishment of the French Open's historic home.

Fans and players will have to wait to until 2020 to see the retractable roof in operation over the court. However, this year sees the tournament bow of Court Simonne Mathieu, a 5,000-capacity semi-sunken arena enclosed by greenhouses.

Spain's Garbine Muguruza, the 2016 champion, had the honour of opening proceedings on the new court against America's Taylor Townsend. The 19th seed marked the occasion with a 5-7, 6-2, 6-2 win.

Venus Williams, the 38-year-old American, faces Ukraine ninth seed Elina Svitolina on the same court later in the day. Williams, runner-up to sister Serena in 2002, made her debut in Paris in 1997.

Also in action on the first day is Italian 16th seed Marco Cecchinato who shocked Djokovic in the quarter-finals in 2018. Japan's Kei Nishikori, seeded seventh, faces France's Quentin Halys on the 30th anniversary of his coach Michael Chang winning the title in Paris.

American seventh seed Sloane Stephens, the 2018 runner-up to Simona Halep, begins against Japan's Misaki Doi. Croatia's 31st seed Petra Martic was the first winner of the 2019 tournament, easing past Tunisia's Ons Jabeur 6-1, 6-2.