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The holder of 15 grand slam titles has not occupied the top spot for more than two-and-a-half years after injuries in 2010 and 2011 saw her drop out of the top 100, bringing predictions of a career end.
However, Williams was clearly the world's best player again during the second half of last year when she won the Wimbledon, Olympic, US Open and WTA Championship titles.
The pinnacle seemed within reach until she was struck by multiple setbacks during last month's Australian Open. Williams turned her right ankle in her opening round, hurt her back while running for a drop shot during her second, and exited in the quarterfinals after one of the most startling defeats of her career, to Sloane Stephens, then outside the top 30.
It was Williams's first loss to a younger American and also, she asserted, her "worst two weeks".
It will have made her keener than ever to return to something nearer her true self during the $2,3-million event in Doha, her first outing since that debacle.
She is seeded second and could have a semifinal with Maria Sharapova, the French Open champion who gave her a very hard final in their last encounter, at the WTA Championships in Istanbul three months ago.
Sharapova has a particularly tough quarter, which contains two former grand slam winners, Samantha Stosur of Australia and Svetlana Kuznetsova of Russia, and a former world number one, Jelena Jankovic of Serbia.
A further incentive is that Williams is only 355 ranking points behind Victoria Azarenka, the world number one, and is offered leapfrogging opportunities by the 900 points which are awarded to the winner.
Much will depend on the extent of Williams's physical recovery.
She reckoned her condition was the worst it had ever been in a grand slam last month, and she will want to show that she is not facing another injury-ravaged sequence.