Serena Williams rallied to successfully defend her WTA Championships title with a three set victory over Li Na in Istanbul.
The American, winning her 11th title of the season, dropped the first set 6-2 but hit back to level the match 6-3 before running away with the decider 6-0.
Williams has lost only four of her 82 matches in 2013 and finishes the year as the top ranked player in the women's game for the third time, achieving the feat in 2002 and 2009 as well.
China's Li was playing in her first WTA Championship final and will finish the year third in the rankings.
"It's been a really long year, I'm really excited as I didn't think I was going to get through this," said Williams.
"I can't believe I won, I was so tired. She played so well. It's such a special moment to finish the year as No 1 and to win the title in the 40th year of the WTA."
Li got off to a better start over a sluggish-looking Williams, who struggled a day earlier to beat Jelena Jankovic and complained later of being exhausted after a long season.
The Chinese, passing Williams almost at will, was quick to break serve for a 2-1 lead and rolled through the first set, which ended with Williams netting a forehand and hitting a backhand passing shot wide.
Williams won a key game at the start of the second set that went to nine deuces and lasted nearly 12 minutes as the American fended off two break points before finally prevailing with a service winner.
Li blasted an ace, her only one of the match, to level at 3-3. But she produced a double-fault and a forehand error to give Williams a chance to serve out the set, which she did at the third attempt.
It was another double-fault by Li that gave Williams a break of serve at the start of the third and the American never looked back.
Williams did have to save five break points, the last one with her sixth ace, before wrapping up the title.