NEW YORK — After practices, Melanie Oudin retrieves tennis balls and sweeps the clay courts at the U.S. Tennis Association’s training center in Queens. She performs these tasks in the shadow of Arthur Ashe Stadium, the site of her greatest accomplishment, close enough to hit with a long forehand, yet far enough for her star turn there to seem like it took place in another life.

At Ashe, when she walks the hallways, Oudin can hear the crowd she enchanted with her surprise quarterfinal run in the U.S. Open nearly three years ago. She can feel the tears that streamed down her cheeks. She can remember the smallest details, which is especially important now, since that run marked the beginning of her precipitous fall from world No. 31 to No. 370.

“It’s good I can remember,” Oudin said. “I look forward to getting back there.”

In recent months, as she inched back toward respectability and obtained a wild-card entry into the French Open were she will play Sweden’s Johanna Larsson in the first round, Oudin, now 20, returned to the USTA training fold.

Once there, she discovered that to overcome burnout and a crisis of confidence, she needed more work, not less.

Oudin arrived in Queens in February, her game in such shambles that one USTA coach, Jay Gooding, told her, “I’m sorry to say, but everyone who plays you expects to beat you now.”

The work began immediately: fitness in the morning, sprints and stairs and endurance workouts; morning practice, mostly drills; match play after lunch; another workout after that.

Oudin hit what seemed like a million balls, and early on, she could hardly walk. She regularly fell asleep at 8 p.m. Coaches often found her with ice bags on both knees, her face streaked with sweat.

She told them, “This is exactly what I need.”

Ashe Stadium is where Oudin catapulted into the national consciousness in the summer of 2009, when she toppled four Russians, including Elena Dementieva and Maria Sharapova, to become the youngest female quarterfinalist since Serena Williams in 1999.

Before the Sharapova match, Oudin and friends discussed how she would celebrate if she actually won. That was how improbable it seemed. When she did win, she screamed and cried and fell to the ground. The next day, hundreds of spectators watched her practice, a Roger Federer-type crowd. Talk shows called. So did magazines. She was 17 years old.

“It’s like one day, you’re normal,” Oudin said. “And the next day, every single person at the tournament knows who you are.”

Oudin thought that she could handle it. Turns out, she thought wrong.

Oudin, who also reached the fourth round of Wimbledon in 2009, knew she could compete at the highest level. She had done that, until, suddenly, she no longer could. A 25-24 singles record in 2010 gave way to a 10-33 mark in 2011. She went 2-8 in Grand Slam singles tournaments after the fairy tale 2009 Open.

The low point came at Wimbledon last year, when Oudin concluded a long stretch in Europe by winning only one game in a first-round singles loss. She took a few weeks off and felt good when she returned, felt rested and ready. Then she lost her next five singles matches, to the point where she started to lose count of the defeats.

Patrick McEnroe, general manager of USTA player development, helped Oudin transfer from the organization’s Florida training center, where she started in November, to the one based in New York for more individual instruction and a change of scenery. After one hitting session, he recognized her major issue, a lack of confidence in movement.

At her best, Oudin is the tennis equivalent of a counterpuncher. What she lacks in height and power, she makes up for in variety and shot selection, what McEnroe described as a high tennis IQ. At her worst, Oudin tried to hit harder, blast more winners, than opponents.

“She doesn’t have that kind of game,” McEnroe said. “She was trying to play too big, and that took her out of her element. We felt like the joy of competing wasn’t there as much. She disappeared, for lack of a better word.”

Her coaches refer to Oudin’s comeback as her second career. She said the split from her longtime coach, Brian de Villiers, who was reportedly mentioned in court documents as a reason for her parents’ divorce, helped shift her perspective. Just as the seven hours of training, six days a week, helped reshape her game.

The climb toward contention remains steep. In the latest rankings, Oudin is at No. 266. She lives not in her own apartment, but with the family of a top-ranked junior. Her coaches considered the French Open entry more of a bonus, as they did not expect her to peak until the U.S. Open or later in the year.

On her end, Oudin believes she is a better tennis player than she was in 2009, by a long shot. She has also examined the trend of recent Grand Slam winners, most of whom are in their late 20s, with far more experience.

At one recent practice, Oudin glided across the court, blond hair pulled into that familiar ponytail. Ashe loomed nearby, so close and so far. Oudin swept the court clean.