Carlos Alcaraz has backed Joao Fonseca to win a grand slam title after the Brazilian's brilliant Australian Open bow.

Fonseca marked his grand slam debut in style on Tuesday, defeating ninth seed Andrey Rublev 7-6 (7-1) 6-3 7-6 (7-5).

The 18-year-old enjoyed a remarkable 2024, which he capped off with a title tilt at the ATP Next Gen Finals.

Fonseca will take on Lorenzo Sonego in round two, and Alcaraz - himself only 21 - sees the sky as the limit for the teenager.

Asked if he had watched Fonseca's match against Rublev, Alcaraz told reporters: "I saw a little bit. I couldn't watch the whole match.

"I saw a little bit at the beginning and the end. What can I say about it? Just incredible.

"The way he played [in] his first grand slam match against his first top 10 [opponent], it's unbelievable.

"The way he approached the match, the way he handled everything, the nerves, the match in general, it was fantastic."

The tennis world is on notice.@carlosalcaraz discusses the arrival and future of Joao Fonseca #AO2025 pic.twitter.com/MWF81AMUoc
— #AusOpen (@AustralianOpen) January 15, 2025

Fonseca is only the second teenager since 1973 to defeat an ATP top-10 opponent in their maiden grand slam match, after Mario Ancic, who shocked Roger Federer at Wimbledon in 2002.

When asked if he thinks Fonseca will go on to compete for a major crown, Alcaraz said: "He's someone that I have to be careful of! He's going to be there.

"This is just the beginning of the year, just one win in a grand slam, but he's going to be there.

"We're going to be putting Joao Fonseca's name on the list of the best players in the world really soon."

Alcaraz beat Yoshihito Nishioka on Wednesday, teeing up a third-round tie with Nuno Borges.