Wimbledon champion Angelique Kerber said the pain from an ankle injury was “not my excuse” after her shock first-round exit at the French Open.

The German fifth seed lost 6-4 6-2 to world number 81 Anastasia Potapova.

The three-time Grand Slam champion said she “did not have much expectation” after pulling out of the Madrid and Rome clay tournaments this month.

Elsewhere, Spanish 19th seed Garbine Muguruza came from a set down to beat American Taylor Townsend 5-7 6-2 6-2.

Muguruza was broken for a second time late in the first set by the world number 83 but breezed through to win the next two sets in the first main draw match on the new Simonne Mathieu court.

The 2016 French Open champion will play Sweden’s world number 172 Johanna Larsson in the second round, following her victory over Slovak Magdalena Rybarikova.

Russian Potapova, playing in her first French Open, faces Marketa Vondrousova of the Czech Republic next.

“My phone is exploding at the moment,” said a delighted Potapova after her surprise win.

Meanwhile, Czech second seed Karolina Pliskova eased into the next round with a straight-set victory over Madison Brengle.

The 27-year-old, who reached the semi-finals at Roland Garros in 2017, won 6-2 6-3 to set up a meeting with Slovakian qualifier Kristina Kucova.

Last year’s runner-up Sloane Stephens also progressed on Sunday, with the 26-year-old American winning a tie-break in the second set to beat Japan’s Misaki Doi 6-3 7-6 (7-4).

• Konta in form and doing the right things – Russell Fuller
• Live scores, schedule and results
• Alerts: Get tennis news sent to your phone

Kerber, who was bidding for a career Grand Slam, had played only three matches in the current clay-court season before coming to Roland Garros.

She admitted two weeks ago she was unsure she would be able to compete.

“At the end I didn’t have much expectation for the tournament. And I think the feeling I had before the tournament was right,” she said after her defeat on Philippe Chatrier court.

“I was able to practise in the last few days really good, but it was not a long clay-court preparation with everything. At the end, I was just happy to at least go on court, playing a match, and of course it is not like I hoped for.”

On whether she was suffering pain, she added: “It is not my excuse, I tried my best. I know there is still a little bit of work to do to play matches 100%, into sliding, to jumping on the foot, and on the leg.”

Roger Federer made a winning return to the French Open with a dominant first-round victory over Lorenzo Sonego.

The Swiss 20-time Grand Slam winner, playing at Roland Garros for the first time in four years, beat the Italian 6-2 6-4 6-4.

He arrived to a standing ovation on Philippe Chatrier court and left with the crowd on their feet in delight.

The 37-year-old will play German lucky loser Oscar Otte, ranked 145th in the world, in the second round.

“I knew I can play very well on clay and I am very happy I did it in straight sets today,” Federer said.

“I missed the French crowd so thanks for the warm welcome today.”

• Kerber suffers shock first-round defeat
• Live scores, schedule and results
• Alerts: Get tennis news sent to your phone

Four years away – 101 minutes to first victory

The rapturous reception he received was the only clue that Federer had ever been away from the Paris clay-court Grand Slam tournament.

The third seed missed the 2016 event with a back injury and skipped the past two clay-court seasons to preserve his body.

He raced to a 4-0 lead in the opening set before Italian world number 73 Sonego finally held his serve.

But while Sonego temporarily stemmed the flow, Federer marched on to claim the opening set in just 24 minutes.

“Two breaks in the first set was very important for me and when I was leading 4-0 I could take more risks and play more aggressive,” Federer said.

He had looked like he was going to race away with the match until Sonego began to find some form when he was a double break down midway through the second set.

A cross-court forehand winner set up three break points for the Italian, all of which Federer saved before Sonego snatched the break when the Swiss double-faulted.

The 24-year-old celebrated the breakthrough as if he had won the match – and was soon fist-pumping again when a delightful lob had Federer well beaten to seal a hold in the next game.

But the brief glimmer of hope for the Italian was soon stamped out as Federer wasted no time in a hold to love to take the second set.

A closely contested third set was effectively decided by a thundering Federer backhand across the court that gave him a break for 5-4 and he went on to wrap up the match when Sonego sent a service return wide in the next game.

Greek sixth seed Stefanos Tsitsipas comfortably beat German world number 110 Maximilian Marterer to reach the second round of the French Open.

The Australian Open semi-finalist broke twice in the opening two sets and clinched the deciding tie-break in a routine 6-2 6-2 7-6 (7-4) victory.

He faces Indian world number 86 Prajnesh Gunneswaran or Bolivian Hugo Dellien, ranked 92, next.

Croat 11th seed Marin Cilic beat Italian Thomas Fabbiano 6-3 7-5 6-1.

The former US Open champion will face Serb Janko Tipsarevic or Bulgarian Grigor Dimitrov in the second round.

• Konta in form and doing the right things – Russell Fuller
• Live scores, schedule and results
• Alerts: Get tennis news sent to your phone

Tsitsipas has been in good form heading into Roland Garros, reaching the final of the Madrid Open following victories over fourth seed Alexander Zverev and five-time champion Rafael Nadal.

He also captured his third ATP title – and his first on clay – when he beat Uruguay’s Pablo Cuevas 6-3 7-6 (7-4) to win the Estoril Open before losing in the semi-finals to Nadal in Rome.

The Greek, who is the rising star on the ATP Tour, also played in clay tournaments in Monte Carlo and Barcelona – winning 13 matches in total on clay before coming to Paris.

“It is quite different to other tournaments I have played. It is slow. It is not too fast, it is fine. I love playing on this court though. It gives you another energy on the big arenas,” said Tsitsipas following his win over Marterer.

“These are the moments that we are practising and dreaming of.”