Serena back to top spot after Safina's withdrawal in Doha

SERENA Williams will finish the year as world number one, having defeated sister Venus after Russia's Dinara Safina withdrew from the season-ending WTA Championships.

 TOP OF THE PILE: Serena Williams back to world number one after Safina withdrawal

Serena was already guaranteed to move back to the top of the rankings before striking a ball against her sibling after Safina threw in the towel against Jelena Jankovic after just two games.

The Russian promptly withdrew from the event citing a back injury, handing Serena the top spot before she went on to defeat Venus 5-7, 6-4, 7-6 (4) in a closely-fought match.

"It's such a great feeling," said Serena, who knew she only had to win one more match in Doha than her Russian rival. "Dinara is such a great player. She must be really hurt, because she never gives up."

Safina, who will be replaced in the White Group by compatriot and first alternate Vera Zvonareva, later revealed she would be sidelined for at least six weeks and could miss January's Australian Open.

"My body just gave up," said Safina. "I did everything possible to play here, but I could not handle this pain anymore.

"I think I should have taken a break after the US Open but I was chasing this number one, so I was fighting with my body."

After exchanging sets by a solitary break of serve, the clash between the Williams' sisters entered a tie-break and while Serena led 4-1, Venus mounted a comeback and forced her younger sister to save a match point at 5-6.

Serena then jumped into a 3-0 lead in the tie-breaker and she converted her first match point with an ace after two hours and 41 minutes of play.

It was defending champion Venus' second straight loss, but she can still reach the semi-finals if she beats Svetlana Kuznetsova and Serena defeats Elena Dementieva.

Venus, commenting on Andre Agassi's drug revelations, said: "His book will probably sell. It seems very interesting, to say the least."