The 39-year-old Djokovic was pushed by 74th-ranked French player Valentin Royer, who is 15 years younger than him, for more than three-and-a-half hours before he reached the third round with a 6-3 6-2 6-7 (7-9) 6-3 victory.
Djokovic said: "It was a very, very difficult match in difficult conditions. A big challenge for me. ... Experience helped me a lot.
"That was really, really hard. I've played two matches and I feel like ​I've played for two weeks."
When Djokovic won a key point early in the fourth set with a forehand that he whipped around the net post from far off the court, the 24-time Grand Slam champion waved his arms toward the crowd inside Court Philippe-Chatrier.
Djokovic wasted a chance to close Wednesday's match out earlier when he missed a backhand long in the third-set tiebreaker then required four more match points in his final service game before a forehand from Royer finally landed in the net to conclude a long rally.
Before arriving in Paris, Royer had earned only one tour-level win across 11 tournaments he played this season.
Djokovic came to Roland Garros with questions over his form after losing in his only clay-court match before the tournament. He was beaten by Croatian qualifier Dino Prizmic at the Italian Open after two months out due to a right shoulder injury.
But Djokovic is playing himself back into form after coming back from a set down to beat Giovanni Mpetshi Perricard, another Frenchman, in a first-round match that lasted nearly three hours.
Djokovic improved to 14-0 in his career against Frenchmen at Roland Garros and reached the third round in Paris for a 21st straight year. He raised the Coupe des Mousquetaires trophy in 2016, 2021 and 2023.
A pair of Djokovic fans inside the main stadium held up a sign with a goat on it - for 'Greatest of All Time' - that read '39 is the new 29.'
Up next for Djokovic is a potentially bigger test against 19-year-old Brazilian Joao Fonseca, who demonstrated his powers of recovery by coming from two sets down to beat Dino Prizmic 3- 6 4-6 6-3 6-1 6-2.
Russian 11th seed Andrey Rublev was given a three-hour workout in the Paris heat in a 6-1 1-6 6-3 7-6 (5) victory over Argentina's Camilo Ugo Carabelli to move into the third round.
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