Melbourne: Serena Williams` status as the world number one is under serious threat going into the Australian Open this week, with three players able to unseat her as the top ranked woman.
The American held on to the top ranking for the entire 2014 season and if she makes the final at Melbourne Park noone can take it away from her.
But if the 33-year-old doesn`t then it could be claimed by either Maria Sharapova, Simona Halep or Petra Kvitova, ranked two, three and four in the world respectively.
Sharapova is the leading challenger and a form player, having won the lead-up Brisbane International, with toppling her long-time arch-rival firmly in her sights.
"Number one is a ranking every player wants to grab and works so hard for," she said.
"There`s a lot of players that have an opportunity to get there, and I`m one of them.
"I am, of course, determined to do that. But by doing that you need to win more matches than the person in first place. So that`s the goal."
Sharapova has two paths to be on top of the world, according to WTA Tour officials.
She can claim the distinction by reaching the final and for two other things to happen -- Williams falling before the semi-finals and Kvitova not beating Sharapova in the tournament decider.
A second way is by the Russian winning the title and Williams exiting before the final.
Halep, who geared up for Melbourne by winning the Shenzhen Open, and Kvitova, who won the Sydney International on Friday, can both become number one as well, but it`s much harder.
They both need to at least win the title -- Halep would also need Williams to be knocked out before the quarter-finals and for Sharapova to fall before the final, the WTA said.
Kvitova would also need Williams to exit before the semi-finals.
The prospect of losing the accolade has 18-time Grand Slam champion Williams fired up and in a fighting spirit.
She won the last of her five Australian crowns in 2010 and is frustrated that a sixth has eluded her for so long.
"I want it, I think, more than anyone else here," she said.