Fonseca, the 2023 US Open junior champion and currently ranked 65th, played his first match in the main draw of a major at the Australian Open in January, when he knocked off No.9 seed Andrey Rublev.
On Tuesday the 18-year-old delighted a loud and overflowing group of spectators at 1500-capacity Court 7 and won the first French Open match of his nascent career, brushing past 30th-seeded Hubert Hurkacz 6-2 6-4 6-2.
In doing so he became the second-youngest men's match winner at the clay-court major in the past 10 years, behind only an 18-year-old Carlos Alcaraz in 2021.
"I'm young, and I'm getting the experience of everything now," said Fonseca "So I'm learning a lot from this circuit and this environment."
Last year's champion at the Next Gen ATP Finals, Fonseca needed just one hour, 40 minutes to wrap up the victory, producing more than twice as many winners, 36, as unforced errors, 15, and repeatedly delivering booming forehands.
"I mean, he's (got) a very powerful game," said Hurkacz, who reached the Wimbledon semi-finals in 2021 by beating Roger Federer in the last match of the 20-time major champion's career. "He's definitely an all-around player and can develop a lot. It's difficult to play against him."
All along, Fonseca heard plenty of support from the Brazilians who haven't had a Grand Slam champion to cheer for since Gustavo Kuerten was winning three French Open titles in 1997, 2000 and 2001.
In the month after the Australian Open Fonseca won his maiden tour-level title in Buenos Aires and he now boasts an 11-7 tour-level season record.
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