Musical chairs

In the eyes of many, the battle for top spot in the women's game could come down to a seemingly never-ending game of musical chairs between Williams, Sharapova and third-ranked Victoria Azarenka of Belarus, the reigning Australian Open champion.

Serena Williams of the US serves the ball to Victoria Azarenka of Belarus during the final match at the Qatar Open tennis tournament in Doha, Feb 17, 2013. [Photo/Agencies]

"Serena is the most dangerous and she is the favorite at this point when she goes into tournaments because she has the most weapons," former world number one Tracy Austin told Reuters.

"She's an extraordinary athlete and I think because she has had some time off in her career, for extended periods where she was either injured or just away from the game, she still has the hunger."

Asked whether anyone could get close to Williams when the American was in prime form, Austin replied: "Azarenka gave her a good show at the US Open last year, losing 6-2 2-6 7-5 in the final.

"Then we thought Serena was on her game at the Australian Open in January and she lost to Sloane Stephens (in the quarterfinals). So it's certainly possible."

Austin, who at 16 became the youngest US Open champion in 1979 before claiming a second US crown in 1981, regards Azarenka and Sharapova as the likeliest challengers to Williams for top spot.

"Victoria has really come through," said Austin. "She got mentally tougher, has more belief, got speedier about the court, got better movement and now she has the two Grand Slams.

"She is the most likely challenger right now. And then you have Maria. She is just a great story because she's already won so much and yet the motivation never seems to dissipate.

"She just seems to love the challenge of trying to improve as a tennis player and I just admire her so much for that because she clearly has won enough, she clearly has enough money."

Austin said she had been hugely impressed by the Russian's fighting spirit after having surgery on her right shoulder in October 2008 before dropping out of the top 100 in the rankings by May of the following year.

"After the surgery, I am sure she was concerned whether she was ever going to get that big weapon of a serve back again, as most of us were.

"But she just kept on fighting and working and believing in herself, won the French Open last year and got back to number one for a short time. It's a really spectacular story."