Brazilian teenager Joao Fonseca secured his first ATP tour title on Sunday by beating local favorite Francisco Cerundolo 6-4, 7-6(1) in the Argentina Open final.

The 18-year-old showed composure beyond his years, winning 73% of his first-serve points to prevail in an hour and 45 minutes on the outdoor clay of the Buenos Aires Lawn Tennis Club.

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

"It'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."

Fonseca became the 10th youngest title winner and the youngest South American champion since the ATP tour began in 1990.

Taking part in his first tour-level final, Fonseca twice served for the match - at 5-4 and 6-5 - only to see 28th-ranked Cerundolo force a tie-break.

The Rio de Janeiro-born right-hander then found another gear, clinching four of his seven points in the tie-break with clean winners, including a superb forehand down the line on match point.

"I want to thank my family, my friends and my sponsors for just helping me achieve my dream, which is to play tennis," he said. "Of course I want to be No. 1, of course I want to win slams, titles, but my dream is just to play tennis, and I'm living it."

Fonseca, who beat four Argentines en route to the ATP 250 title, is expected to see his world ranking rise to 68 from 99 on Monday.