Borna Coric announced himself as a coming force in men's tennis by knocking out Lukas Rosol in the opening round of the US Open.
The 17-year-old Croatian was marked out as one to watch a number of years ago and all indications are that he is the real deal.
Coric came through qualifying to reach the main draw at a grand slam for the first time only a year after winning the junior title at Flushing Meadows.
Rosol, the 29th seed, won an ATP Tour title in Winston-Salem on Saturday but Coric dominated the clash, winning 6-4 6-1 6-2.
The teenager, who is ranked 204th in the world, said: "It's an amazing feeling. I came here and I was only thinking about getting in the main draw. That was my first goal.
"I said to myself, 'if I achieve that, that's going to be perfect'. Now actually winning against a guy who is top 30, it's just unbelievable.
"I don't have any pressure. If everyone is looking at me, I'm even more excited about everything because I'm going to prove to everyone that I'm a good player."
After Nick Kyrgios' run at Wimbledon, where the 19-year-old beat Rafael Nadal to reach the quarter-finals, this is another sign that the next generation may break through significantly faster than their predecessors.
"It's unbelievable from him," said Coric of Kyrgios' exploits. "It doesn't mean anything to me but it showed that younger players can play with the top 10 or top 20."
Coric has a British coach, Ryan Jones, and splits his time between Croatia and London.
He has also been getting tips from some of the greats of Croatian tennis, including Goran Ivanisevic, Ivan Ljubicic and Marin Cilic.
Coric is not the only teenage talent making waves from the country, with Donna Vekic and Ana Konjuh ones to watch on the women's side.
"I think it's because in Croatia it's not so easy," he said. "We don't have the best conditions to train. We don't have a lot of money. So you need to be tough if you want to make it. We are not spoiled. We are working hard."
Coric next meets Victor Estrella Burgos from the Dominican Republic, who also posted his first ever grand slam win, but at the age of 34.
Fourth seed David Ferrer dropped a set to Bosnia's Damir Dzumhur but recovered to win 6-1 6-2 2-6 6-2.
John Isner once again leads American hopes in the men's tournament and he began his campaign with a 7-6 (7/5) 6-2 7-6 (7/2) win over American college champion Marcos Giron.
It has been a tough few years for US men's tennis and last year no home player reached the fourth round for the first time in the tournament's long history.
Isner, the only American seed, said: "I try not to focus on some of the negative things that people say about American tennis.
"I know I get the brunt of it a lot, because if I win and play well it's because I have a big serve and I can hit my forehand pretty well and that's it. But if I lose, it's because that's all I can do. Sometimes I feel like I can't win no matter what.
"I know what I'm capable of, but it's up to me to play well and advance in this tournament."
Tenth seed Kei Nishikori has been sidelined by a toe injury but shook off any rust quickly in a 6-2 6-4 6-2 win over Wayne Odesnik, while there were also straight-sets wins for Richard Gasquet and Fabio Fognini.