Yearender Tennis: Golden year for Andy Murray, regrets for Rafa Nadal

After her battles with serious injury and health problems in recent years, Williams appears as hungry as ever and will be the woman to beat when the new season begins at the end of December.

"It's amazing that I'm still considered like one of the top players to beat. For me it's the ultimate honour and the ultimate compliment," Williams said in Istanbul before suggesting that the best might still be to come.

"I definitely think I can improve," said the 15-times major winner. "The day I feel that I can't improve, I think that's the day I should probably hang up my racquet."

Should Nadal return to his full force in 2013 the top four of the men's game looks set in stone, although several players have shown in 2012 that they can shake up the top order.

Juan Martin del Potro enjoyed an injury-free year and got back to the form that saw him win the 2009 U.S. Open final while Canada's Milos Raonic, Japan's Kei Nishikori and Poland's Jerzy Janowicz will be worth watching.

On the women's side, 2011 Wimbledon winner Petra Kvitova looks the most likely to threaten the leading trio, although consistency remains her undoing.

In team tennis the Czech Republic dominated.

Their men beat Spain to win the Davis Cup for the first time as an independent nation - reward for Tomas Berdych, one of the most consistent performers on the tour throughout the year - while the women retained the Fed Cup, beating Serbia.

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