On the women’s side, the only truly dominating player this decade has been Serena Williams. Her return to the sport full time last year after being sidelined by injuries has re-established a more natural order in women’s tennis, with two Grand Slam winners, Maria Sharapova and Victoria Azarenka, serving as her worthy, if not yet equal, adversaries. But Wimbledon blew that order into disarray — none of the four semifinalists had ever won a Grand Slam — and showed how erratic the women’s game can still be.

As the U.S. Open begins this week, Li senses an opportunity. At 31 years old, she still possesses great foot speed and thunderous ground-strokes, including what many consider to be the most cleanly struck backhand in the game. In the past, Li has tended to fade in the later majors from a lack of fitness and focus. (At the U.S. Open, she’s gotten to the quarterfinals only once, in 2009.) But this summer, after watching her at Wimbledon, I followed Li back to Beijing to witness up close her demanding midseason training regimen with her coach, Carlos Rodriguez. Li is making a big push to make the world’s Top 3 and to win another Grand Slam. “Anybody could win the U.S. Open this year,” Li said. “Why not me?”

Born in 1982, Li Na was, like many Chinese athletes, pushed into sports against her will. Her father — a former badminton player whose career had been cut short by the chaos of the Cultural Revolution — was the “sunshine of my childhood,” she said. Even so, he gave his daughter no choice when he enrolled her at age 5 in a local state-run sports school. Though she was a strong athlete, her shoulders were deemed too broad and her wrists not supple enough to excel at badminton. A coach persuaded her parents that she would have a better chance in a sport that few Chinese at that time had ever seen. “They all agreed that I should play tennis,” she said, “but nobody bothered to ask me.”

From the beginning, Li chafed at the harsh strictures of the state-run sports machine. China’s juguo tizhi — or “whole-nation sports system” — churns out champions by pushing young athletes to their limits every day for years on end. The first time Li defied her coach came at age 11, when, on the verge of collapse, she refused to continue training. Her punishment was to stand motionless in one spot during practices until she repented. Only after three days of standing did Li apologize. She continued training for her father’s sake — “His love was my source of strength,” she said — even though her coach never uttered a word of praise in their nine years together.

When she was 14, her father died of a rare cardiovascular disease. She was playing in a tournament in southern China at the time, and her coach didn’t tell her for several days, waiting until the competition was over. “It is my deepest pain that I did not make it to say goodbye to him,” Li wrote in her autobiography. Her mother sank into debt, and Li remembers being driven to win in tournaments so that she could earn small bonuses to fend off creditors.

Despite the turmoil, Li’s tennis flourished. Her first national junior title came just months after her father’s death. The following year, she was invited to a 10-month Nike-sponsored training program in Texas. After her return, she told an interviewer that she aimed to make the Top 10 in the world, and by early 2002, her goal actually seemed attainable: the 20-year-old was ranked No. 1 in China and had even climbed, at one point, into the world’s top 135. And then she disappeared.

Without telling any of her coaches, Li slipped out of the national training center one morning later that year. To avoid suspicion, Li said, she carried only a small bag of necessities. On the desk in her dorm room was a letter she had written to tennis authorities requesting an early retirement. The note didn’t elaborate on her reasons: the burnout from excessive training, the outrage at her coaches’ attempts to squelch her romance with a male teammate named Jiang Shan, and the debilitating period which the team leader wanted her to play through by taking hormone medicine.