Serena Williams of the U.S.celebrates defeating compatriot Taylor Townsend during their women's singles match at the U.S. Open tennis tournament in New York August 26, 2014. REUTERS/Shannon Stapleton
#6 Serena Williams Total earnings: $22 million Prize money: $11 million Endorsements: $11 million REUTERS

The World No. 1 status of Serena Williams is under serious threat at the 2015 Australian Open this week. Maria Sharapova, Simona Halep and Petra Kvitova are all vying to unseat Williams as the top ranked World No. 1 tennis player at the first Grand Slam tournament of the year.

Serena Williams held the World No. 1 spot for the entire season last year, but now she might lose the most coveted title to three challengers: World No. 2 Maria Sharapova, World No. 3 Simona Halep and World No. 4 Petra Kvitova. Sharapova, who is the leading challenger of Williams, revealed that the number one spot is a ranking that every player wants to achieve and she is determined to get there by winning more matches than the World No. 1.

On the other hand, Serena Williams, who is playing to win her sixth Australian Open title, revealed that she wants the title more than anyone else and she's going to fight hard to get it. "My preparation is okay, I'm not very happy with it, but I'm never really happy about my practice or preparation so maybe that's a good sign," Williams said. "I definitely feel better now than I did a couple of weeks ago, but I still want to improve some things."

Maria Sharapova of Russia is set to face Petra Martic of Croatia, while Serena Williams will not play until Tuesday. Simona Halep of Romania will be in action against Karin Knapp of Italy.

Sharapova can earn the World No. 1 rank if she reaches the finals and if Williams doesn't qualify for the semi-finals and Kvitova fails to beat her in the tournament decider, according to WTA Tour officials as reported by Manila Bulletin. If Sharapova wins the title and Williams exits before the finals, the Russian will be the new World No. 1. Meanwhile, Halep and Kvitova can be World No. 1 if they win the Australian Open title and the 18-time Grand Slam champion fails to qualify for the quarterfinals and Sharapova falls before the finals.

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