Brazilian teenager Joao Fonseca became the 10th youngest champion in ATP Tour history when he swept past home hope Francisco Cerundolo in the final of the Argentina Open.

The 18-year-old, ranked 99 in the world and playing in his first tour-level final, came through 6-4, 7-6 (7/1) against his 28th-ranked opponent.

Fonseca twice unsuccessfully served for the match but regrouped to claim victory in the tie-break in a frenzied atmosphere in Buenos Aires.

The 2024 ATP NextGen champion is the youngest male player from South America to win a tour title while his victory will also see him rise to 68 when the new rankings are released on Monday.

"Unbelievable week, even in Argentina there are some Brazilians cheering for me," Fonseca said on court.

"That's just amazing. Every Brazilian, everyone from their country wants this support from your own country. For me, this moment that I'm living is just unbelievable," he added. "Of course I want to be number one, of course I want to win Slams, titles, but my dream is just to play tennis, and I'm living it."

Cerundolo, seeking his fourth career title, was broken in the seventh game of the first set and fought off Fonseca when the teenager served for the trophy at 5-4 and 6-5 in the second.

However, the Brazilian impressively held his nerve in the tie-break and celebrated his triumph by collapsing in joy on the dusty, clay surface.

Fonseca made his maiden final the hard way – in Friday's quarter-finals he saved two match points to defeat Mariano Navone in a match six minutes shy of three hours.

In all, he defeated four Argentinian players on the road to the trophy.

He had already announced himself on the scene in January when he came through qualifying at the Australian Open and defeated top 10 player Andrey Rublev in the first round. (AFP)