Safina suffers Doha injury blow

Safina could lose her number one spot to Serena Williams

Dinara Safina's future involvement in the Sony Ericsson Championships is in doubt after she was forced to withdraw from her opening round-robin encounter.

The world number one broke down with a back injury after just two games of her match against Jelena Jankovic in Doha.

If Safina is forced to miss the rest of the season-ending event, Serena Williams will become world number one.

Earlier on Wednesday, sixth seed Victoria Azarenka lost 1-6 6-4 7-5 to fourth seed Caroline Wozniacki.

Number eight seed Jankovic was beaten by sixth seed Azarenka in their first match on Tuesday.

606: DEBATE It looked as if there was a major problem, maybe she should have scratched and let the alternate play. She must have known Duggie

"It's really unfortunate. Dinara said she had hurt her lower back," said Jankovic after the 13-minute match.

"I wished her well for her recovery. We all have problems with our bodies at this time of the year."

The season finale is split into two groups of four, with the top two in each group making the semi-finals and the eventual champion taking home US$1.55m (£944,000).

Serena Williams, who plays her sister Venus later on Wednesday in the White Group, only has to win one more match than Russia's Safina to overtake her in the rankings.

Serena beat Svetlana Kuznetsova in her first match on Tuesday, while Venus was beaten by Elena Dementieva.

Denmark's Wozniacki saved a match point in the final set to see off Azarenka in their Maroon Group encounter.

Azarenka was up a break four times in the third set but failed to finish things, letting her 19-year-old opponent break back each time.

Wozniacki, who made just two winners in the first set, saved a match point with Azarenka leading 5-4 in the third before finally holding serve in the decider.

The Dane broke again for 6-5 after the Belarussian was docked a point for smashing her racquet, and Wozniacki sealed victory with a service winner after two hours and 58 minutes.

After her win, Wozniacki, playing her first match in the event, seemed to be affected by the sore hamstring that forced her to retire from the Luxembourg Open last week.

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