A month after reestablishing herself as the unquestioned No. 1 player in the world, Serena Williams could lose the No. 1 ranking at the WTA to the woman she has beaten 15 straight times.

Tennis.com reported that new No. 2 Maria Sharapova, fresh off a victory at the China Open, is within reach of Williams' No. 1 ranking as the two head for the WTA Finals in Singapore later this month.

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Williams has 7,146 points accumulated; Sharapova has 6,680. The winner of the round-robin earns 1,500 points, according to tennis.com. The runner-up earns 1,090 points, while a semifinalist gets 690 points.

The issue for Williams is that she withdrew from the China Open in Beijing, citing a knee injury. If for some reason she doesn't play in the WTA Finals, then Sharapova doesn't need to win the event. Competitors earn 70 points per round-robin match, with the winner earning an additional 90 points.

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That means Sharapova would need just three wins to surpass Williams.

Or Sharapova could close the gap by entering the Kremlin Cup in Moscow, with 470 points going to the winner.

But that's not in Sharapova's thought process.

"I don't think I've ever done that in my career, add a few tournaments to my schedule to gain points, in order to find a certain ranking. Never in the juniors, never in the pros," she said, according to tennis.com. "Most important is to be healthy.

"Of course, it's an incredible achievement if I could do it, considering where I started the year. But in the meantime I know I've had a great year and I'm going to go into the last tournament that I have just wanting to elevate my performance, use this week as a great stepping stone in the right direction, and finish it off well."

Sharapova started the year ranked No. 9 after coming off a shoulder injury. She has titles at the French Open, Madrid and Beijing.

Williams, meanwhile, really didn't have a consistent season, failing to get past the fourth round in the first three legs of the Grand Slam until turning her season around with a win at the U.S. Open.

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