Jannik Sinner reacts as he cools himself with water during a break in his second round men's singles match against Juan Manuel Cerundolo at the French Open in Paris on Thursday as temperatures rise to 91 F. (AP photo)

PARIS — Not since Rafael Nadal was winning his record 14 French Opens had a player come to Roland Garros as such an overwhelming favorite to win the clay-court Grand Slam.

Jannik Sinner had won everything there was to win in tennis over the past three months: five straight Masters 1000 titles — three of them on clay — and 30 straight matches.

And with Carlos Alcaraz, his biggest rival, out due to an injured right wrist, it seemed almost a foregone conclusion that Sinner would raise the Coupe des Mousquetaires trophy and complete a career Grand Slam.

That’s why Sinner’s meltdown amid the Paris heat wave was so stunning Thursday — especially after he came within just one game of concluding his second-round match in straight sets when he led 5-1 in the third.

The top-ranked Sinner struggled with dizziness and was beaten by 56th-ranked Juan Manuel Cerundolo 3-6, 2-6, 7-5, 6-1, 6-1 after wasting two chances to serve for the match.

“I didn’t feel very well on court,” Sinner said. “I struggled, starting to feel very dizzy, very low on energy. … In the beginning, I was hitting very clean, very good, and then I just kind of hit the wall.

“I didn’t have energy, really. I was very, very flat. The whole body. I don’t remember last time I felt this weak,” Sinner added.

Sinner said that when he woke up on Thursday he “didn’t feel very well.”

Sinner bent over on the clay court in apparent exhaustion multiple times and was hardly even running for shots as the match wore on, resorting to drop shots and serve-and-volley tactics to try and shorten the points.

He attempted to cool himself with a hand-held fan on changeovers and put bags of ice around his neck.

The temperature at the start of the match was 84 degrees F and rose to 90.

“It was warm but not crazy warm,” Sinner said. “I feel like it was quite OK to play. Really it was nothing against the heat, nothing against the weather. It was just me today, but it happens.”

Cerundolo didn’t celebrate too much when it was over, just producing a little wave to the crowd.

“It’s tough for him,” Cerundolo said. “I couldn’t win more than three games by set. So I think I was a little bit lucky. … He was deserving to win in this match.”

Sinner’s previous loss came Feb. 19 in the Qatar Open quarterfinals. He had won five straight Masters titles while dropping just three sets.

In other matches, fifth-seeded Ben Shelton was upset by 62nd-ranked Belgian opponent Raphael Collignon 6-4, 7-5, 6-4; and Frances Tiafoe required nearly five hours to overcome Hubert Hurkacz 6-7 (5), 7-6 (5), 6-4, 6-7 (1), 6-4.

In women’s action, Naomi Osaka put on another fashion show for her walk-on before beating Donna Vekic 7-6 (1), 6-4.

Defending champion Coco Gauff beat Mayar Sherif 6-3, 6-2; and top-ranked Aryna Sabalenka — the runner-up last year — defeated Elsa Jacquemot 7-5, 6-2.

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AP Sports Writers Samuel Petrequin and Jerome Pugmire contributed to this report.

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AP tennis: https://apnews.com/hub/tennis