MELBOURNE, Australia (AFP) — A series of jaw-dropping upsets of top 10 players at the Australian Open by fearless teenagers has fueled excitement at the future of men’s tennis as the old guard fades into history.

With Rafael Nadal and Andy Murray retiring last year and Novak Djokovic in the twilight of his record-breaking career, the torch has already passed to the likes of Jannik Sinner and Carlos Alcaraz.

But the giant-killing exploits in Melbourne of Joao Fonseca, Learner Tien and Jakub Mensik signaled another generation are already knocking on the door.

Highly-rated Brazilian Fonseca, 18, thrust himself to the world’s attention with a first-round upset of ninth seed Andrey Rublev, and 19-year-old Czech Mensik matched him by stunning sixth seed Casper Ruud.

They were outdone by American Tien, 19, who caused a massive shock in beating fifth seed and three-time Australian Open finalist Daniil Medvedev in a five-set epic.

It is the first time two teenagers or more have beaten top-10 players at a major since 2006, when Djokovic and Murray achieved the feat at Wimbledon.

“New blood is coming,” declared Mensik, already ranked 48, after his first round Ruud win.

“For the fans, for tennis, for everything, it’s really great.”

Nine-time Grand Slam-winning doubles champion John Fitzgerald called Mensik’s game “frightening.”

“At times we all get ahead of ourselves but this kid to me looks like he could be a future Grand Slam champion. He’s a serious player,” the Australian great said on commentary duties at the tournament.

“He’s here to stay... what a game he has, it’s a frightening game.”

As Mensik went about his business, Fonseca was hogging the global headlines.

The Brazilian is considered one of the hottest talents in years, announcing his arrival in December by beating Tien to become the youngest winner of the NextGen tournament since Sinner claimed the title five years ago, also aged 18.

Mensik was also at the event in Saudi Arabia.

With his seismic ground strokes and unshakeable confidence, Fonseca was a class above Rublev before nerves got the better of him when he met Italian journeyman Lorenzo Sonego and was knocked out in round two.

Undeterred he said: “Of course, my expectations are bigger now. I want more and more.”

“I think that’s the mentality of the champion.”

Alcaraz tipped him to be among the world’s top players “really soon.”

“What can I say about it? Just incredible,” the four-time Grand Slam-winning Spaniard, himself only 21, said.

“We’re going to put Joao Fonseca’s name on the list of the best players in the world really soon.”

Djokovic, a 24-time Grand Slam champion, said he had been monitoring Fonseca’s progress and was equally impressed with the youngster who is set to break into the top 100 when the new rankings are released.

“I’ve been following his rise, and I just love how he plays the big points. Courageous, very clean hitter, all-around player,” he said.

“Brazil is a huge country. Super important for our sport to have a very good player coming from Brazil.”

Tien’s victory over Medvedev saw him become the second youngest American man in the Open era to reach the third round in Melbourne — behind only 14-time Grand Slam winner Pete Sampras in 1990.

Born to Vietnamese parents in California, he said the success of Fonseca and Mensik had driven him to greater heights.

“It was definitely pretty inspiring. They obviously got those wins before I played my match (against Medvedev), said Tien, currently ranked 121.

“Just trying to almost join them. I think just seeing them, the wins they’ve had this week, just adds a little bit more belief that it’s possible.”