Former French Open champion Stan Wawrinka continued to struggle with form and fitness as he was dumped out in the first round by Guillermo Garcia-Lopez on Monday,  a defeat which will send his world ranking plummeting, but Novak Djokovic cruised through in straight sets.

Wawrinka, who lost to Rafael Nadal in last year’s final and won the 2015 title, was beaten in a five-set thriller 6-2 3-6 4-6 7-6 (7/5) 6-3 by the Spanish World No.67 on Court Suzanne Lenglen.

The 33-year-old has been plagued by a knee injury and arrived at Roland Garros having won just one match on clay in Geneva last week, his first event in three months.

The defeat means that the three-time Grand Slam champion will slip from 30th in the world to outside the top 250 after the tournament, having failed to defend the ranking points he gained in 2017.

“There is no frustration (at rankings slip). It’s just tough,” said Wawrinka.

“But again, I knew from the beginning that it will take a long, a lot of time to get back. I knew that from the surgery that it will take a year at least to get where I want to be.”

There were worrying signs for his fans when he pulled up and called for a medical timeout after just six games, but he played down fears he had caused further damage to his already troublesome left knee.

“My knee is good. I blocked something else at the beginning of the first set, and that’s why I had to ask,” he said.

The 23rd seed found his rhythm from nowhere after a poor first set, crunching two massive forehands to break for a 3-1 lead in the second.

A fired-up Wawrinka duly levelled the match, and saved a break point to serve out the third set after breaking in the opening game, as 34-year-old Garcia-Lopez threw his racket to the ground in disgust.

The match looked to be all but over when Wawrinka broke in game five of the fourth set, but he became ragged and Garcia-Lopez forced a decider by edging a tie-break.

Wawrinka’s form totally deserted him in the fifth set, and Garcia-Lopez comfortably wrapped up victory.

Serbian star Djokovic had little trouble in reaching round two, though, seeing off Brazilian world number 134 Rogerio Dutra Silva 6-3 6-4 6-4.

The 12-time Grand Slam champion dropped serve three times and will have to markedly improve to challenge Rafael Nadal in the latter stages of the tournament, but he was still far too good for Dutra Silva on Court Philippe Chatrier.

“It was good to start this year with a win. I wasn’t at my best, he played with a lot of spin. I didn’t play very well, but I won in three sets,” said the 20th seed, who will next face David Ferrer or Jaume Munar.

Former world number one Victoria Azarenka’s return to Grand Slam tennis lasted just two sets as the Belarusian slumped to a 7-5 7-5 loss to Katerina Siniakova.

Azarenka, who missed much of last season after being embroiled in a custody battle over her son, was broken to love in the 12th games of each set to be dumped out by the Czech world number 57.

It was Azarenka’s first Grand Slam match since losing to Simona Halep in the Wimbledon fourth round last July, but she still believes she can return to the top of the game.

“No doubt about it. Maybe not today, but no doubt about it,” the now-world number 82 insisted.

Petra Kvitova also found life hard, but the two-time Wimbledon champion fought back from a set down to beat Paraguay’s Veronica Cepede Royg 3-6 6-1 7-5 on Court Philippe Chatrier.

The 28-year-old Kvitova is one of the favourites to win a maiden Roland Garros title after winning four titles this season, including on clay in Prague and Madrid.

“I’ve won 12 matches straight on clay, but I’m still a long way from Rafa,” she said in reference to Rafael Nadal’s upcoming bid for an 11th men’s singles crown.