Injuries hurt Williams sisters rankings

DAYTONA BEACH, Fla., Oct. 25 (UPI) -- Serena and Venus Williams each dropped another notch in the world women's tennis rankings just as the season-ending WTA Championships get under way.

The Williams sisters will be the only Top 10 players not at the special invitation event, which begins Tuesday in Doha, Qatar. Serena beat Venus in the 2009 WTA Championships final.

Serena and Venus qualified for the 2010 tournament but ended their seasons because of injury. Serena Williams suffered a foot injury that required surgery shortly after she won at Wimbledon. Venus Williams is out with a leg injury.

With the injuries keeping them sidelined, the sisters' rankings have slipped. Serena Williams, No. 1 as recently as the Oct. 4 rankings, dropped to third behind No. 1 Caroline Wozniacki and new No. 2 Vera Zvonareva.

Venus Williams, third on Oct. 4, is now fifth as Kim Clijsters has moved into the No. 4 spot.

Francesca Schiavone retained the No. 6 spot but Samantha Stosur moved ahead of Jelena Jankovic and into seventh. Jankovic is eighth followed by ninth-ranked Elena Dementieva and Victoria Azarenka, who is coming off a win Sunday at the Kremlin Cup.

Dementieva, Schiavone, Stosur and Wozniacki will compete in the Maroon Group round-robin this week while the White Group has Azarenka, Clijsters, Jankovic and Zvonareva. The top two finishers in each group advance to the semifinals. If a player goes through Sunday's finals unbeaten, she will collect $1.55 million.