Mauresmo, the defending champion, scored a gripping 4-6, 7-6 (7/3), 6-2 win which meant elimination from the yellow group for double former champion Martina Hingis.

Henin-Hardenne will now face US Open champion Maria Sharapova in Saturday's semifinals while Mauresmo will take on Kim Clijsters.

Sharapova eased into the last four by beating Russian compatriot Svetlana Kuznetsova 6-1, 6-4. Clijsters made sure of her place in the semi-finals by seeing off Elena Dementieva 6-4, 6-O.

Returning from a shoulder injury, Mauresmo started off here looking as if she might not last the pace following a straight sets loss to Nadia Petrova but instead she has ended up winning her group with gutsy wins over Hingis and now Henin-Hardenne.

"I am very happy the way I dug in both yesterday and today. I kept believing in myself despite the bad start. I'm proud of the way I played," said the Frenchwoman who will slide off the world top spot after 34 weeks on Monday despite taking her career series with Henin-Hardenne to 6-5 in her favour.

Either Henin-Hardenne or Sharapova will finish the year as world number one.

Sharapova, who took just 68 minutes to see off Kuznetsova in a red group encounter, landed these championships two seasons ago.

"I don't know if I am playing the best tennis of my life," said Sharapova.

"But I'm a better player than I was a year or two ago."

After Henin-Hardenne got her nose in front and then went a break ahead in the second it seemed as if Mauresmo was done for, but she saved two break chances against her at 4-4 and then won the ensuing tiebreak when French Open champion Henin-Hardenne began to crack, serving up two double faults.

Mauresmo then waltzed through the decider against the women she beat for her two Slam titles this year.

Henin-Hardenne herself had suffered an injury-plagued build up, not playing for two months owing to wrist problems.

She also had to miss out in the last two editions of the championships with injury.

Despite Friday's reverse the diminutive star can secure the world number one spot if she wins her semi, but if she does not then Sharapova can catch her at the line if she reclaims the title.