Donald Young reacts after winning his match against Juan Ignacio Chela of Argentina on Sept. 4. His advancement into the fourth round marks his best performance in a Grand Slam event. (Charlie Riedel/AP)

This year at the U.S. Open, Donald Young has been wearing a yellow shirt that dazzles like the floodlights on Broadway. And there’s nothing random about it.

“I like to wear flashy things if I’m feeling good,” said Young, 22, who’s enjoying his best performance in a Grand Slam tournament, having reached the fourth round. “If I’m not feeling good, I want to wear something neutral to not be seen in.”

Touted since age 14 as the next American tennis phenom, Young has spent most of his pro career fading into the background, his results never living up to the hype of a brilliant junior career.

But after seven years of an often self-defeating slog through the pro ranks, Young is finally playing up to his potential.

On Wednesday he’ll face No. 4 Andy Murray for a place in the U.S. Open quarterfinals. The match was scheduled for Tuesday, but driving rain forced the cancellation of both day and night sessions.

The gutsy play of young Americans was among the top story lines of the tournament’s first week, with 18-year-old Jack Sock reaching the second round, and 21-year-old Irina Falconi and Christina McHale, 18, making it as far as the third round.

But Young’s performance, marching into the fourth round as a wild card ranked 84th in the world, had its own dramatic arc — both unexpected and overdue. And it has been cheered by those who have followed his struggles up close, such as fellow Americans Andy Roddick and Mardy Fish, and those who have watched from arm’s length.

Said five-time U.S. Open champion Roger Federer, who was anointed Europe’s next great sporting genius as a teen: “[Young] has been real good at a very young age. I think his coming into [the pro] tour was rather complicated. Getting a lot of wild cards and getting a lot of help creates a lot of pressure, right?

“So that’s hard to live up to. I really feel that, because I had expectations, too. But I had them when I was 17, 18. 19. He maybe had them when he was 15, 16, 17. It’s a big difference. Seems like he’s making his move now, and he has had some good wins . . . [And] he’s backing it up with good play.”

Young was just 16 when he became the world’s No. 1 junior, though he had turned pro by then. He won the 2005 Junior Australian Open title and the 2007 Junior Wimbledon title.

But for all this promise, Young couldn’t hold his own against grown men on the pro tour.

And the defeats ate away at the confidence that was such a part of his game — and that of any tennis player’s game.

Said veteran sports agent, tennis promoter and former pro Donald Dell, who has followed Young’s career: “It’s the classic case of a tremendously talented 14- or 15-year-old coming into the pros, in my opinion, way too fast. What happens when he turns pro, everybody on the circuit tries to beat his brains out because they want to destroy his confidence. They’re afraid he’s going to get better and better.”

Young says he remembers loving all the attention he got as a top junior. Everyone was excited about his talented. Everyone wanted him to win — particularly the racket manufacturers, clothing representatives and corporate sponsors that were so eager to invest in his future.

“When it doesn’t happen, you’re really disappointed — more so because you want to win yourself,” said Young, who in one stretch lost 14 consecutive matches on the ATP Tour before dropping down to the Challenger ranks, where he lost to players ranked in the 300s in obscure towns a world away from New York. “Then you start thinking about what are people thinking when you’re playing. And that’s definitely not the way to go about it.”

He considered quitting and going back to school, where his friends were having such fun. And he took to wearing neutral colors on court, happy to fade into the background rather than be singled out as the sport’s most famous bust.

But “a light came on,” as Young puts it, in the past year. For too long, Young admitted in an interview last week, he felt he knew everything.

“I felt I didn’t have to work as hard as everyone else,” he added.

So he decided that if he wanted different results, he needed a different approach. Instead of working out one week in the offseason, as he typically did, he spent a month at the USTA training center and, for the first time in his career, worked out twice a day in the gym and on court.

It paid dividends this summer at Washington’s Legg Mason Tennis Classic, where Young reached his first ATP semifinal.

“Back-to-back wins over high-caliber guys was great for my confidence,” Young said. “It made me feel like after this time that I really belonged.”

Now, instead of walking on court and trying simply not to get beat, Young takes the court with a different attitude.

“I feel I can actually win,” he said, a tone of awe in his voice. “That’s a great feeling to go on the court.”