Fonseca took the tennis world by storm after a herculean performance in dismantling 10-time grand slam quarter-finalist and ninth seed, Andrey Rublev in a straight sets opening-round victory on Tuesday night (AEDT).
It came after the Brazilian swiftly moved through Australian Open qualifying with three straight-set wins - incredibly for the loss of a mere 12 games.
The 18-year-old’s stocks have continued to rise since he took out the 2024 ATP Next Generation Finals in December - where he claimed the title, defeating Tien in the final, despite being the lowest ranked player in the tournament.
Fonseca then went on to win his second ATP Challenger title at his very first event of the season in Canberra, during the opening week of 2025.
Despite bowing out in the second round to Lorenzo Sonego in five sets on Thursday night (AEDT), the 18-year-old from Rio has deservedly stolen many of the headlines.
Australian master coach, Darren Cahill also revealed that his charger - world number 1 Jannik Sinner - has massive wraps on Fonseca.
"I asked Jannik what ranking he thought Joao Fonseca would be in at the end of the year and he said, 'in the top 25,'" Cahill said.
And if those words aren’t strong enough for the current world number 113, then you only need to look at Fonseca’s Instagram followers, which have risen from 295,000 to almost 700,000 just a few days after the Rublev victory.
But the next gen performances at AO 2025 haven’t stopped with Fonseca’s run - you only need to look at what Tien was able to do against world number 5 and 2021 US Open champion, Daniil Medvedev.
The American, who only turned 20 a month ago, produced some inspired tennis to defeat the three-time Australian Open finalist in five sets during their second round match, and hilariously celebrated by eating a pizza after the pair finished close to 3am on Friday morning (AEDT).
"It was either going to be celebratory or a binge eat … it feels better, it's more celebratory, for sure," Tien said.
The 18-year-old became the youngest American man to make the Australian Open third round since Pete Sampras 35 years ago.
Tien now faces Frenchman, Corentin Moutet for a place in the Round of 16 later on Saturday afternoon (AEDT).
Moutet’s fellow countryman, Arthur Fils impressed at Melbourne Park during his own run to the third round.
Fils, who also played in the 2024 ATP Next Generation Finals alongside Fonseca, Tien and Michelsen, was forced to retire during his round of 32 match against another Frenchman, Ugo Humbert.
He was trailing Humbert two sets to one and decided to call it quits due to a foot-strapping issue, after going down an early break in the fourth set.
But 20th-seeded Fils should be proud of his efforts at AO 2025, after producing two solid four-set wins to make the third round.
Meanwhile, giant-killing Michelsen secured the best grand slam run out of the next gen quartet to date, after sealing his place in the last 16 at Melbourne Park on Saturday (AEDT).
The 20-year-old American followed up his shock first round win over two-time grand slam finalist, Stefanos Tsitsipas by also defeating 19th seed and dual grand slam semi-finalist, Karen Khachanov.
Michelsen became the youngest American - since Sampras and Andre Agassi at the 1990 US Open - to record multiple top-20 wins at a grand slam.
"I played unbelievable in that match. I don't even really know what's going on," Michelsen said.
And with those words it’s clear - these four players, all aged 20 years and under, are simply fearless.
The future of tennis is certainly bright and these next gen stars are here now to shake things up.
