Alexander Zverev has shown he can win run-of-the-mill tournaments and Masters titles, too. He's shown he can make it to the second week of a major.
What everyone is watching - and waiting - for now is a grand slam semi-final, final or trophy.
"Sascha Zverev," said Washington Open co-founder and chairman Donald Dell, using Zverev's nickname after the 21-year-old German won the hard-court tune-up for the US Open a second consecutive year, "is the future of pro tennis."
Zverev is seeded No.4 at Flushing Meadows, where play begins Monday, and is widely considered the likeliest member of the latest generation of tennis pros to make a deep run at this US Open after getting to his first major quarterfinal at the French Open.
Zverev isn't alone, though. He's part of a crop of youngsters who might be ready to take over the sport from the old hands who have dominated it for more than a decade.
Stop us if you've heard that before, though.
"They're still there," Zverev said about the so-called Big Four of Roger Federer, Rafael Nadal, Novak Djokovic and Andy Murray.
"Obviously, they're still contenders for every single tournament they play."
It's worth noting that Zverev is one of only five active players who's won at least three Masters events. The others? Federer, Nadal, Djokovic and Murray, who are all in their 30s and have combined to win 49 of the past 54 Grand Slam titles.
Men's tennis just keeps skewing older: Last month at Wimbledon, all four semifinalists were in their 30s, the first time that happened at any slam in the half-century of professional tennis.
But look closely, and there are signs that change could be on the way.
"They're definitely knocking on that door," Federer said.
"... and there is some exciting talent around."
In Washington this month, for example, Zverev's victory over Australian 19-year-old Alex de Minaur made for the youngest final on the ATP World Tour since a 20-year-old Nadal beat a 19-year-old Djokovic at Indian Wells in 2007.
And the ages of the two losing semifinalists in Washington? Andrey Rublev is 20; Stefanos Tsitsipas turned 20 the following week at the Toronto Masters, where he became the youngest player to beat four top-10 opponents at one tournament since the ATP World Tour was established in 1990.
"Four 'NextGen' players in the semifinals. That's amazing for tennis, I think," Zverev said in Washington, referring to the marketing campaign the tour uses to promote up-and-comers.
"Me being the oldest - that never happened to me before. It's interesting. And I like where tennis is going. I like the development of the other young guys. It's going to be interesting to see what it'll be like in the future."
Agreed. Zverev is one of seven men who are 21 or younger and ranked in the top 50.
