DOHA: Serena Williams, having stripped naked for an American magazine shoot, can lay bare her simmering frustration over losing her world number one ranking at the WTA Championships which start Tuesday.

Despite winning the Australian Open and Wimbledon titles in 2009, taking her Grand Slam collection to 11, Williams has again been displaced at the top of the women's game by Russia's Dinara Safina who has yet to capture a major.

Williams's fourth career stopover at the top of the rankings lasted just two weeks.

Coming in the slipstream of her notorious, foul-mouthed US Open meltdown, which could still spark a Grand Slam ban, the 28-year-old American will be on a very personal mission at this 4.55 million dollar season-ending tournament.

The eight-woman field of Safina, Serena and Venus Williams, French Open winner Svetlana Kuznetsova, Elena Dementieva, Caroline Wozniacki, Victoria Azarenka and Jelena Jankovic, also boasts intriguing sub-plots.

Wozniacki, the world number six from Denmark, finds herself embroiled in a WTA probe following her controversial injury withdrawal in Luxembourg last week.

Players are also desperate to lay down markers ahead of the 2010 season before Kim Clijsters, the shock US Open champion, and fellow former number one Justine Henin start chipping away at newly-minted reputations after coming out of retirement.

Serena Williams has never hesitated to mock Safina's number one status already this year.

"My motivation is to win another Grand Slam and stay No. 2, I guess. I'd rather definitely be No. 2 and win Grand Slams in the past year than be No. 1 and not have any," she said after her Wimbledon triumph over sister Venus.

Williams comes into Doha also desperately trying to move on from her now infamous US Open semi-final defeat to Clijsters where she launched a furious, verbal assault on a female line judge.

The outburst followed being called for a foot fault which handed Clijsters match point; the ensuing penalty point confirmed Williams's defeat.

A 10,000-dollar fine and an apology have not halted an ongoing ITF investigation.

"I think it's important for people to learn from things that they've done in the past and I feel like I've completely learned and I would never do the same thing," said the American, no doubt happy that the official from Flushing Meadows has decided against making the trip to the Middle East.

Safina, runner-up at the Australian and French Opens, has defended her position in the rankings, claiming it's a reward for playing more tournaments and performing consistently well at them.

For Williams, the Russian's promotion will appear particularly galling, coming on the back of Safina's second round defeat in Beijing against Zhang Shuai, a Chinese player ranked 226th in the world.

Venus Williams, who routed Safina for the loss of just one game in the semi-finals at Wimbledon, is the defending champion here and will be playing in her ninth WTA Championships.

Wozniacki and Azarenka, who was in the spotlight in the summer for her ear-piercing screeching at Wimbledon, are Championship newcomers.

Jankovic, who was world number one at the start of the year, was the eighth and final qualifier, squeezing through in Moscow last week.

The eight players are split into two groups of four with the top two in each making the semi-finals.

The champion takes home 1.55 million dollars.