''Everything became harder,'' Henin said. ''I felt, deep inside, something was getting out of my grasp.''
She lost 6-4, 6-0 to Maria Sharapova in the Australian Open, then 6-2, 6-0 to Serena Williams at the Sony Ericsson Open in April—the worst loss for a top-ranked player in nine years.
At last week's German Open, Henin lost 5-7, 6-3, 6-1 to Dinara Safina. Then she pulled out of this week's Italian Open, citing fatigue.
''At the end of the match in Berlin, (retirement) all of a sudden was there as something evident,'' Henin said.
Her announcement came a day after one of the greatest female golfers in history said she's quitting: Annika Sorenstam, owner of ten major titles and one of six women to complete a career Grand Slam in her sport, is walking away at the end of the season.
Henin, however, won't have any sort of farewell tour. She is retiring immediately.
''I had reached my limits, and I feel strong and relieved that I could take this decision,'' she said. ''There are plenty of things that I can do. There are no regrets. I did everything I had to do in tennis.''
In addition to her four French Open titles, Henin won the Australian Open in 2004, and the U.S. Open in 2003 and 2007. She has been ranked No. 1 since Nov. 13, 2006, except for a seven-week period last year when Sharapova held the top spot, and won nearly $20 million in career prize money.
''She was a great champion,'' said Williams, who lost to Henin in a contentious 2003 French Open quarterfinal, ''and she gave me a world of trouble.''
The only Grand Slam title to elude Henin is Wimbledon, where she was runner-up in 2001 and 2006.
''Winning Wimbledon would not make me happier than I am,'' she said.
Winning again at Roland Garros would make no difference, either, no matter how much that event means to her. Henin dedicated her first victory there to her mother, who died of cancer when Justine was 12. When Henin won there last year, it capped a reunion with her father and siblings, from whom she'd been estranged for several years.
''That was awesome. It was a great feeling, and I am going to keep that feeling forever now,'' she said. ''I won Roland Garros four times, three times in a row. I don't have to live that moment again. I know how it was.''
Throughout her career, Henin has had to beat the odds.
With her 5'5", 126-pound frame, she had to figure out how to deal with foes who could hit the ball harder. With a superb one-handed backhand, amazing speed, and grit, she rose to the top of the sport.
''She always challenged herself to play her best tennis no matter what the circumstances. She was just a real fighter, so I think that was really what made her the best,'' Venus Williams said.
''Justine Henin will be remembered as one of the all-time great champions in women's tennis, and a woman who made up for her lack of size with a will to win and fighting spirit that was second to none,'' WTA Tour CEO Larry Scott said. ''It is rare that an athlete leaves at the very top of her game in this day and age, but Justine has always played by her own rules, in the very best sense of those words.''
Henin was away from the tour for months at a time in 2004 and 2005 because of an energy-sapping blood virus and assorted injuries, including to her knee and back. In early 2007, she divorced from Pierre-Yves Hardenne and dropped his last name.
Throughout last season, Henin said she had finally found a balance in her life between personal self-fulfillment and doggedly pursuing tennis titles.
Now it appears that changed. Perhaps she took note when Kim Clijsters—another Belgian who was ranked No. 1 and won a Grand Slam title—retired at 23 last year. Clijsters has since married and become a mother.
Dressed in a simple white t-shirt and jeans, her brown hair in a ponytail, Henin spoke in French for nine minutes before taking questions Wednesday. She never lost her composure and held the microphone firmly.
The news conference was at the Justine N1 academy in a village about 20 miles outside of Brussels. It has a smattering of her beloved clay courts, where she wants to train and coach youngsters.
Family and children may come, but for now, and for once, there is no rush.