Britain's Cam Norrie is out of the French Open after retiring injured when a set and a break down in his round-one contest against the unseeded Adolfo Daniel Vallejo.
Norrie, who was seeded 20 and came into the clash with a rib complaint, missed four chances to win the opening set before losing a tie-break 9-7 to Paraguay's Adolfo Vallejo.
He lasted only two more games after that setback, shaking hands with his opponent when 2-0 down in the second set.
Fellow Brit Jacob Fearnley later fell to Argentina's Juan Manuel Cerundolo 6-2 7-6 (7-0) 7-6 (9-7) in the first round as his campaign came to a swift close.
The result means there are no remaining British players in the men's draw at Roland-Garros after Jack Draper's pre-tournament withdrawal due to injury.
"It's a tough feeling right now," said Norrie. "I thought I would be ready but it was obviously too soon.
"I think I was just a little bit mentally tired, not having the ability mentally to put the pain away, the pain aside, and just play point for point."
With the grass season only a week away, Norrie was concerned about potentially risking a longer absence from the tour by struggling on.
He will get the injury checked again in London on Wednesday, and admitted he may not make the ATP event in the Netherlands beginning on June 8, but is confident of playing in the HSBC Championships at Queen's Club the following week.
"That will be my goal," said Norrie. "And I'm really excited to go play. Maybe it's good timing. I can get a chance to rest."
Tournament favourite Jannik Sinner got his French Open off to a predictably smooth start as he beat Frenchman Clement Tabur in a 6-1 6-3 6-4 straight-sets win.
It took just 30 minutes for the Italian to take the first set against his wild-card opponent, who has never been ranked above 171 in the world.
Despite a promising early third-set break for the hometown hero, Tabur always looked second best to the world No 1, who took his first step to a career Grand Slam at the age of just 24 and extended his win streak to 30 successive matches.
Sinner will face Cerundolo - who knocked out Fearnley - in the second round on Thursday.
Daniil Medvedev suffered a five-set loss to 97th-ranked Australian opponent Adam Walton.
Walton, who received a wild-card invitation from tournament organisers, beat Medvedev 6-2 1-6 6-1 1-6 6-4.
"It's huge," Walton said of the victory in his on-court interview, adding a win over Medvedev in Cincinnati last year had given him the confidence to repeat the feat.
"I knew I could do it and I believed, so I'm just happy with my performance. I'm really excited right now."
French teenager Moise Kouame made the perfect start to his French Open career with a 7-6 (7-4) 6-2 6-1 win against veteran Marin Cilic.
Kouame won one day after the 39-year-old Frenchman Gael Monfils made his last appearance at Roland-Garros.
At 17 years and two months old, Kouame became the youngest player to win a Grand Slam match since Australia's Bernard Tomic reached the 2009 Australian Open second round at the age of 16.
He is also the youngest player to advance past the first round at Roland-Garros since Romania's Dinu Pescariu achieved the feat in 1991 at 17 years and one month old.
He raised his arms in triumph and tilted his head back after defeating the 37-year-old Cilic, who won the 2014 US Open, finished runner-up at two other majors, and reached the French Open semi-finals in 2022.
The ATP Tour said No 318-ranked Kouame became the first man born in 2008 or later to win a Grand Slam match, and the crowd on a sun-baked Court Simonne-Mathieu showed their appreciation by chanting "Mo-ise! Mo-ise! Mo-ise!" and clapping in between.
"It's not easy to stay in the present without thinking of the score," Kouame said. "It wouldn't have been possible without the huge help you [the crowd] gave me."
In March, he became the youngest winner in Miami Masters history when he beat Zachary Svajda in the first round - earning a congratulatory message from Djokovic.
Meanwhile, Stefanos Tsitsipas, the 2021 runner-up to Djokovic, was leading 6-2 3-0 against Alexandre Muller when his French opponent retired.
Muller wiped away tears as he left the court and later said he injured his right calf, three months after injuring his left calf.
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