ISTANBUL -- Serena Williams rallied past Li Na 2-6, 6-3, 6-0 to win the WTA Championships on Sunday and complete a dominant season.
In winning her career-high 11th title of 2013 and fourth WTA Championships, a fatigued Williams fought through a slow start and swept the final nine games before 16,457, the largest single-session crowd here. Williams finished the season 78-4 (.951), the WTA's highest single-season winning percentage since Steffi Graf went 75-2 (.974) in 1989. She also set the women's single-season record with $12.4 million in earnings, the third most in tennis history. Only three other players -- Roger Federer, Rafael Nadal and Novak Djokovic -- have made more than $10 million in a season.
"It was an awesome year of tennis," Williams said. "I'm really happy that I was able to finish it off."
Williams, who struggled to a three-set win over Jelena Jankovic in the semifinals on Saturday, looked sluggish again at the start of the match. Li rolled through the first set quickly behind creative net play and fantastic shot-making, particularly on her backhand.
The turning point came in the first game of the second set. Li earned two break points, but when she couldn't convert in the 24-point game, her belief and energy began to slip away.
"Serena understood she was making some tactical errors," coach Patrick Mouratoglou said. "It's a combination of things. She was tired, she was serving 50 percent indoors. Fifty percent against Li Na is very difficult. And I think she was opening up the court too early in the rally. She was going forehand cross-court. She was opening for no reason to Li Na's backhand and Li Na was killing her.
"She stayed calm, she figured out what she was doing wrong, and she started doing things right. And her serve came back. Altogether, she managed to switch the match in her favor."
It was a disappointing end to an outstanding week for Li, who won four matches in four days and pushed Williams in the final.
"I think I was working so hard to prove myself to be [at that high] level," Li said. "After one and a half sets, I was feeling a little bit tight."
Despite ending her season with a bagel set, Li says she will take nothing but positives from making her first WTA Championships final, at age 31, and finishing the year ranked a career-high No. 3. the highest for any Asian player in history. She had her chances against Williams (she went just 3 for 15 on break points) and didn't help herself on her serve, hitting 10 double faults.
Li's coach, Carlos Rodriguez, was pleased with her commitment to get out of her comfort zone and come to the net even when she was behind.
"She played for me a kind of level of tennis that she's not used to playing, going to the net," he said. "I don't know if you understand how hard it was for her to do what she did today. To go to the net not against Jankovic, it's against Serena. The most feared player for years. And try to have the courage to go and serve and volley and have some success. I think emotionally and mentally she spent a lot of energy there."
While the new tactic still doesn't come automatically for Li -- who was 7 for 12 on serve and volley points and 10 of 18 at the net -- she's committed to adding it as a new dimension to her changing game.
"I was nervous a lot, of course," Li said. "I was nervous about what I should do and when I should do it. So even today's match I was also very happy about serve and volley. I don't know how many times I come to the net, but not so many mistakes. So I think I should continue for next year," she said, smiling.
Williams' turnaround just added to the mountain of evidence collected over the course of her incredible season that while others may have the skill to challenge her, Williams' mental strength is second to none.
"When you feel the way she feels at the moment and the opponent is playing at that level, she has to believe," Mouratoglou said. "To find a way to switch the match you really have to believe and you really have to refuse to lose this one. That is something she really has and that makes the difference between her and most of the players."
Williams, who won two Grand Slams among her 11 titles, will finish the season No. 1 for the third time in her career. But she wasn't ready to declare this her best season, not when she won three major titles in 2002.
"I live to win Slams," Williams said. "I mean, obviously I'm so excited to be the WTA champion, and I think I have a top three [season]. I can't say it's the best. I can't say it's not the best. I don't know."
While there was some talk of their ambitions for 2014, Williams and Mouratoglou agreed it's now time for a break.
"I don't think it's the fact that she played more," Mouratoglou said when asked about her struggles this week with mental and physical fatigue. "It's the fact that she stayed focused for all the matches, all the year. She's used to playing half the matches with half the focus. Can you imagine the effort it took her to do what she did this year?"
Williams will reward herself with a minimum two-week break away from the cold -- somewhere she can enjoy some bikini weather.
"I definitely won't be hanging out with my buddy Wilson for a while," she said, laughing, referring to her trusty racket. "We need some time apart, even though I love him."
Williams' win derailed Asia's chance to dominate the Championships, which are moving to Singapore next year. Hsieh Su-Wei and Peng Shuai defeated Elena Vesnina and Ekaterina Makarova to win the doubles title.