LIMELETTE, Belgium – The determination that helped Justine Henin beat bigger, stronger opponents time and again was fading. So she decided "to stop fooling myself and accept it."

Henin retired from tennis Wednesday, an abrupt ending to a career in which she won seven Grand Slam singles titles and spent more than 100 weeks ranked No. 1. At 25, the Belgian became the first player to quit the sport while atop the WTA rankings.

Henin announced her decision at a news conference 1 ½ weeks before the start of the French Open, where she has won the last three titles and four overall.

Put simply, she realized she was burned out.

"I always based everything on this motivation – this flame – that was in me. And once I lost that, I lost many, many things," Henin said.

At 5-foot-5 ¾, 126 pounds, Henin was able to beat stronger opponents with a superb one-handed backhand, amazing speed and grit.

"She was a great champion," said Serena Williams, who lost to Henin in a contentious 2003 French Open quarterfinal, "and she gave me a world of trouble."

After reaching the final at each Grand Slam event in 2006, Henin won 10 tournaments in 2007, including two majors. But this season, her legs felt heavy when she should have been dancing in the backcourt.

"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 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 to Dinara Safina, 5-7, 6-3, 6-1. Then she pulled out of this week's Italian Open, citing fatigue.

After the loss to Safina, Henin said retirement became "something evident."

Though she never won Wimbledon, losing the finals in 2001 and 2006, Henin said she leaves without regrets.

"I did everything I had to do in tennis," she said.