Last weekend Justine Henin-Hardenne reached number one after winning the French Open and the U.S. Open. She is 21.

Both women are slight but whereas Hingis, plagued by an ankle injury, appeared to give up in the face of a new army of power-hitters, Henin-Hardenne has adapted her game, her body and her mind to the challenge.

After finding tennis oh-so-easy in 1997 and 1998, Hingis was blown off course and increasingly off the court by Venus Williams. The Swiss won her last Grand Slam in Australia in early 1999 and when Serena "arrived" at the end of 2001, Hingis suddenly became an anachronism in women's tennis.

Her clever, chess-like approach could not withstand the Williams sisters' cudgelling from both sides of the court and, as her legs gave her increasing problems, she was unable to change her game to arrest the decline.

At Wimbledon in 2001, Hingis lost in the first round for the second time in three years. Venus Williams, the defending champion, charged into the final where she met Henin-Hardenne, very much a surprise finalist.

PHYSICAL DISPARITY

No one could miss the obvious physical disparity between the two women and Henin-Hardenne, after recovering from losing the first set 6-1 to win the second, ran out of strength in the third to go down 6-0.

Unlike Hingis, the Belgian decided that if you can't beat them, you should try and join them. Over the past two years she has made herself more able to slug it out from the baseline for long periods and in the build-up to this season she worked in Florida with Pete Sampras's former trainer Pat Etcheberry.

This season she has been a revelation, physically at her peak as she showed at Roland Garros by defeating Serena Williams in the semi-final and fellow Belgian Kim Clijsters in the final.

Serena took her revenge in the Wimbledon semis before beating her sister in the final. With both Williamses absent through injury at Flushing Meadows, Henin-Hardenne won the title by beating Clijsters in the final again.

"I'm not afraid anymore about the power of the other players because I'm powerful too. I think that everybody knows it right now," she said.

Whereas there were always question marks over Hingis's mental strength after her tantrums at the French Open and Wimbledon in 1999, Henin-Hardenne's has never been in doubt.

No stranger to personal difficulties and tragedy as a child, she has the look of a warrior and never gives up, an aspect of her personality which seems to spook Clijsters in particular.

SPORTING FEAT

Henin-Hardenne's recovery to win the U.S. Open final, after being put on a drip after her exhausting semi-final defeat of Jennifer Capriati, was one of the feats of the sporting year.

The Belgian is also strengthened by the support and advice she gets from the small entourage of her husband Pierre-Yves and her coach Carlos Rodriguez.

With hindsight, Hingis's confidence never recovered from her split in 1999 with her mother and coach Melanie Molitor following her defeat in the French Open final by Steffi Graf.

They patched up their differences but she never won another major title.

While Henin-Hardenne basks in being number one, she will be rated the best player in the world only when she beats Venus and particularly Serena on a regular basis.

Neither of the sisters has been seen on the tour since the Wimbledon final -- Venus hurt her stomach during the tournament and Serena had a knee operation in August. In addition they are mourning their elder sister who was shot dead last month.

Clijsters, number one before Henin-Hardenne, believes Serena remains the best player around and says both sisters are missed.

"They've had a huge influence on how the game has changed. They made it more athletic and powerful and forced all of us to get better. I hope we see them back soon," Clijsters said.