“The Unlikeliest of American Teenagers,” is how the New York Times described Jared Donaldson, in one of the most backhanded of compliments, when the Rhode Island native  came out of qualifying to reach the third round at the US Open in 2016.

Thirteen months later, Donaldson is no longer a teenager. More important, he’s no longer the most unlikely of the young U.S. men’s brigade to succeed.

True to form, the no-nonsense, nose-to-the-grindstone Donaldson has started his Asian swing early. While his fellow Next Genners—including Alexander Zverev, Denis Shapovalov, and his countryman Frances Tiafoe, who is ranked 15 spots below him—were yukking it up at the Laver Cup last weekend, Donaldson was preparing to play in front of sparse crowds at the 250 event in Chengdu, China.

And true to form, he fought his way through to the quarterfinals of that event the hard way, with three-set wins over Stefanos Tsitsipas and Kyle Edmund, before falling in another three-setter to Denis Istomin. The wins moved the 20-year-old two steps closer to qualifying for the inaugural Next Gen Finals in Milan. Donaldson is currently sixth in the race to that eight-man, 21-and-under event, and first among the young U.S. men, ahead of the more celebrated Tiafoe and Taylor Fritz.

“I knew that if I played well, if I played my game, I had a really good chance to win the match,” said Donaldson after beating Edmund, a young British player who has always been considered more likely to succeed. “At the end of the day, each match is a new day, it’s a new match.”

Donaldson’s words weren’t as provocative or off-the-cuff as those that come out of Nick Kyrgios’s mouth during any given interview. But that’s true of the American’s game as well; he can’t afford to be as loose, in attitude or playing style, as the Aussie. Donaldson isn’t the most powerful, or talented, or athletic, or physically imposing of the new generation. He doesn’t have Kyrgios’s waterfall serve or Zverev’s elegantly lethal backhand or Tiafoe’s darting speed or Jack Sock’s dive-bombing forehand. Donaldson does everything pretty well, but there’s nothing easy or especially eye-catching about his shots. He has to work for everything he gets; even his aces look effortful.

The upside of having to work for a living is that, if you’re a certain type of person, you learn to enjoy doing just that. So far Donaldson, who moved from No. 105 at the start of 2017 to a career-high No. 51 in August, has been among the most diligent players of his generation. A former student of Taylor Dent’s who now works with Jan-Michael Gambill and Mardy Fish, he has logged a lot of yards on court this season, and a lot of miles off of it. He’s learning the way most people learn: The hard way.

Donaldson has played Challenger tournaments in Hawaii, San Francisco, and Sarasota, and has crashed out in the first round at eight main-tour events, including the Australian Open and French Open. But as any neophyte pro trying to establish himself must do, he has put his head down and moved on from each defeat. Unlike some of his fellow Americans, Donaldson, who trained for a time in Argentina, played a full European clay-court schedule this spring, qualifying for Madrid and Rome. That work began to pay off more handsomely on faster courts over the summer. Donaldson reached the round of 32 at Wimbledon, the round of 16 in D.C. and Montreal, and the quarterfinals in Cincinnati.

Every other day in August, it seemed, Donaldson was on our televisions in another grueling battle. What I came to like about his game is the way he plays with force rather than flash. Donaldson keeps everything in front of him and takes the simplest route he can find to winning a point. While Kyrgios’s motivation waxes and wanes, and Sock’s concentration has peaks and valleys, Donaldson commits to every point. He leaves you with no doubt about his desire.

But desire isn’t always enough. In the Chengdu quarterfinals yesterday, it was Istomin who was able to dictate when he needed to, who had the X-factor forehand and easy power to take over rallies. In the most important moments, he could elevate his game to a place Donaldson couldn’t quite reach.

Donaldson’s strong summer also ended in slight disappointment at the US Open. It was in another dogfight, naturally, this time in the second round with Lucas Pouille. Donaldson came back from two sets down to take the match to a fifth, and a packed and noisy house on Court 17 was ready to help him across the finish line. But he couldn’t make it; Pouille, bigger and stronger than Donaldson, turned the rallies back in his favor and won 6-4.

Still, I liked that the American swallowed his bitterness and didn’t go for a drive-by handshake, as forgivable as it would have been in that moment. Instead, Donaldson looked Pouille in the eye and barked a heartfelt “Good luck.” His manner said he thought he had done everything he could, but it just hadn’t worked out this time. Donaldson isn’t afraid to put himself on the line and come up short. That’s not true of every player, even at the sport’s highest levels.

“There’s room for improvement, which is good,” Donaldson said after his loss in New York. “The fact that I come off the court and say I know there’s things to work on is a good thing, because if I had nothing left to work on, then I’d be in trouble losing that match.

“It’s obviously disappointing. But there’s always tomorrow...I just got to remember it’s a long road. I got to go back [and] work on those things and get better, come back next tournament, come back next year, and be a better player.”

If you’re a a fan of U.S. tennis, there isn’t much more you can ask. And with that attitude, Donaldson’s success is looking a little less unlikely with each passing month.