RIO DE JANEIRO (AP) — Teenage tennis sensation João Fonseca frustrated his home fans at the Rio Open in a first-round loss Tuesday, two days after winning his first ATP title.

Fonseca lost 6-1, 7-6 (4) to No. 60-ranked Alexandre Muller of France, making 34 unforced errors and appearing to be exhausted during the match.

The 18-year-old Brazilian won his career first title at the elite level with victory in the Argentina Open final on Sunday.

Muller will meet Argentina’s Tomás Martin Etcheverry in the next round.

“It was tough to play against such a great player and perhaps 5,000 (fans), but I’m very happy to get the victory today,” Muller said. “I was feeling calm in half of the match. I didn’t take my chances to take the break in the second set and then he was playing better and better. I played a great tiebreak to finish.”

Teenage sensation Fonseca loses in the first round in Rio days after winning his first ATP title | iNFOnews.ca — France’s Alexandre Muller returns the ball to Brazil’s Joao Fonseca during a match at the Rio Open tennis tournament in Rio de Janeiro, Tuesday, Feb. 18, 2025. (AP Photo/Bruna Prado)

On the weekend, Fonseca became the first man born in 2006 or later to win a top-level ATP singles title, the 10th youngest champion in ATP Tour history and the youngest South American player to win a title in the ATP Tour era (since 1990).

Last year, the rising star reached the quarterfinals of the tournament in Rio, an ATP 500, and finished off 2024 by winning the Next Gen ATP Finals in December.

He moved up 31 spots to No. 68 in this week’s rankings after his win in Buenos Aires.