Kim Clijsters's pursuit of the year-end number one ranking received a boost when third ranked Maria Sharapova was placed in Lindsay Davenport's round robin group for the WTA Tour Championships.

The second ranked Belgian lies just 155 points behind Davenport in the world rankings, but does not have any points to defend at the event starting today, after sitting out the championships last year with a wrist injury.

American Davenport is defending 214 points, while last year's winner Sharapova is protecting 684 points.

Davenport and Sharapova's Green Group in the eight-woman round robin event is completed by Switzerland's Patty Schnyder and Russia's Nadia Petrova.

Clijsters's Black Group also contains Frenchwomen Amelie Mauresmo and Mary Pierce as well as Russian Elena Dementieva.

The event opens today when Clijsters faces Pierce, who she thrashed 6-3 6-1 in the US Open final two months ago for her first major victory.

"Kim has been incredible on hard courts this year," Pierce said of the Belgian, who has won a WTA-Tour high nine events this season.

Sharapova will then take on Schnyder before Davenport faces Petrova.

Tomorrow, Pierce takes on Dementieva, Davenport plays Schnyder and Mauresmo will meet Clijsters.

The two top players in each group will advance to Saturday's semi-finals.

The 18-year-old Sharapova became the youngest winner of the tournament last year, but is currently nursing a right pectoral injury which forced her to pull out of Philadelphia last week.

She is receiving treatment twice a day in a desperate bid to regain fitness.

Clijsters is the only 2005 grand slam winner in the draw. Australian Open champion Serena Williams is out with a knee injury, as is her sister, Wimbledon winner, Venus.

French Open champion Justine Henin-Hardenne pulled out with a hamstring injury.

Venus Williams would have been the tournament's first alternate, but decided not to risk further injury.

France's Nathalie Dechy has taken her place.