Two Asian teenagers have advanced to the second round of the US Open, set to make warnings of a rising young generation of stars come true on tennis’ biggest stage.

Japanese qualifier Yoshihito Nishioka outlasted France’s Paul-Henri Mathieu 6-4, 2-6, 6-7 (7/9), 6-1, 6-2 after three hours and 22 minutes in sweltering heat while South Korea’s Chung Hyeon ripped Australian James Duckworth 6-3, 6-1, 6-2 in 96 minutes.

Chung, ranked 69th, and 128th ranked left-hander Nishioka – both 19 – are the lone remaining teens among 10 that reached the men’s main draw, the most at the US Open since 12 teens made the lineup in the 1990 tournament.

One of them, Pete Sampras, won his first of 14 Slams at age 19.

“We didn’t have one generation like this for a while. They are here now. That’s good for tennis,” said Spanish star Rafael Nadal, who won the first of his 14 career Slam titles at age 19 at the 2005 French Open.

“The best player will be the one that improves. That’s the thing that will make the difference for this new generation.”

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Nishioka, who turns 20 on September 27, will face Brazilian 30th seed Thomaz Bellucci in the second round and there is a possibility he could meet third seed Andy Murray in the third round.

It was the first main-draw Slam victory for Nishioka, who made his Slam debut at last year’s US Open. “I’m very happy to win the first round because it’s the first time I’ve won in a Grand Slam,” Nishioka said. 

Swiss fifth seed Stan Wawrinka will be the next foe for Chung, who fired 10 aces in advancing without facing a break point. “He’s really good mentally,” Duckworth said of Chung.

“He doesn’t get down when something goes wrong. He has won a lot of matches to get into the top 100. That has to build up a lot of confidence.”