Justine Henin-Hardenne secured a place in the semi-finals of the WTA Championships and remained on course to claim the year-end number one spot with a 6-4, 6-4 win over Russia's Nadia Petrova on Thursday.
The French Open champion's victory means that the in-form Maria Sharapova will now have to win the tournament and hope the Belgian does not make the final if she is to deprive her of ending the year as number one.
"It's a great feeling to qualify for the semis," the Belgian said after the match.
"I missed the last two editions because of injury and I'm back after a few weeks off so it's great to be back at the top of the tree.
"I'm not going to change my goal which remains to win every match and get into the final and not worry about being number one."
Amelie Mauresmo, who lost her opening match to Petrova, got her bid to defend her title back on track when she battled her way from a set down to beat Martina Hingis 3-6, 6-1, 6-4 in an enthralling encounter in the yellow group.
The Frenchwoman will join Henin-Hardenne in the semis if she beats the Belgian in her final round-robin match on Friday, but defeat will mean that Hingis progresses to the last four. Petrova is out no matter what happens.
Kim Clijsters bounced back from an opening defeat against Sharapova to blow away Svetlana Kuznetsova 6-1, 6-1 in just 45 minutes and give herself a strong chance of making the semis in the red group.
"I got a few early breaks and that gave me the confidence to carry on," said the Belgian who made a winning return to action after two months out in Hasselt last weekend.
Clijsters plays Elena Dementieva and Sharapova meets Kuznetsova in the final round-robin matches on Friday.
BREAKS EXCHANGED
Neither Mauresmo nor Hingis looked happy on their serve in the opening set of their match as they exchanged four breaks in the first six games.
But the Swiss gained the upper hand when she cracked the Mauresmo service once again in the eighth with the help of a brilliantly disguised drop shot to take a 5-3 lead and then served out to take the set.
Mauresmo, who bagged grand slam victories at Australia and Wimbledon this year, rallied at the start of the second, breaking the Hingis serve after a wonderful lob to take a 2-0 lead and rattled through to take the set 6-1.
She kept up the momentum at the start of the decisive set, racing into a 4-0 lead, but Hingis refused to fold and fought back to trail 5-4 and even earned a break point as Mauresmo was serving for the match.
It was too big a mountain to climb, however, and despite a few nervous moments Mauresmo managed to serve out for the win.
"She started to get a little tired after the first set and I was more aggressive," said the Frenchwoman. "The main thing is that I won and I'm still alive in the group."
Henin-Hardenne, who beat Hingis in her opening match after a two-month injury lay-off, recovered from a slow start to see off her opponent in straight sets.
Petrova got off to a promising start when she broke Henin-Hardenne's serve in the second game, but the Belgian hit back with a double break in the third and fifth to take the set.
It was level-pegging in the second until Henin-Hardenne used her superior court craft to pressure Petrova into a succession of errors on her serve and break in the seventh game.