On another sweltering afternoon in Paris, Djokovic began in cruise control, breaking his young opponent in the opening game of the match and twice more across the opening two sets as he built a 2-0 lead.
Although Djokovic was broken himself in the eighth game of the first set, he responded in style with a hold to love while in the second, he soared to his crowd-pleasing best, pointing to the sky and gesturing for Court Philippe-Chatrier to raise the noise after belying his age to chase down a drop-shot before stretching for a forehand winner.
As in his second-round meeting with Valentin Royer, Djokovic’s level dipped in the third set but on this occasion, he was unable to reassert his dominance.
He became increasingly vocal in the frustration he directed at himself and his coaching team and looked fatigued, leaning over his towel box in exhaustion on several occasions while, at the opposite end of the court, Fonseca crunched booming forehands and toyed with the 39-year-old with multiple drop-shot winners.
Djokovic came out fighting after taking a lengthy break before the decider but, although he struck the first blow – breaking Fonseca in game four, it was the teenager – playing a fifth set for just the third time in his career – who rose to the occasion as the match reached its crescendo.
After hitting just 11 winners across the opening two sets, he struck 22 to Djokovic’s 14 in the fifth, including three drop-shot winners in quick succession – which elicited pained smiles from his opponent to produce the decisive break at 5-5.
Djokovic earned a break point – his 16th – as Fonseca served for the match but the Brazilian nervelessly fired down three successive aces to secure a remarkable comeback win at the first attempt.