Maria Sharapova's power failure

Maria Sharapova knows she needs to regain her power tonight as she tries to bounce back from defeat in her opening match at the WTA Championships in Istanbul.

The world No2 faces China's Li Na, having lost 6-1, 7-5 to Australia's Samantha Stosur at the round robin end-of-season event for the game's top eight women.

Sharapova was a doubt for this tournament after twisting an ankle earlier this month and admits she is not yet up to speed.

"Sam was much more explosive than I was and used her slice really well," said the Russian. "It's obviously tough to come back after a month and compete at this level."

World No1 Caroline Wozniacki, who beat Agnieszka Radwanska 5-7, 6-2, 6‑4, faces Vera Zvonareva tonight.