Serena Williams sure her best years are yet to come

Serena Williams believes her best years may still be ahead of her after she ended 2013 in record-breaking style on Sunday.

The 32-year-old American successfully defended her WTA Championships title, beating Li Na, 2-6, 6-3, 6-0, to finish 2013 with a 78th victory against just four losses, and 11th title of the year.

Williams finished the campaign with prize money of $12,385,572, shattering the all-time women's record set last year by Victoria Azarenka, who won $7,923,920.

It's also the third-highest single season prize money total in tennis history, men's and women's -- only Novak Djokovic's 2011 and 2012 totals are higher.

She is the fourth player ever to win four or more titles at the season-ending event and the oldest champion.

Williams is also the first player to win 11 WTA titles in a season since 1997 when Martina Hingis won 12.

Worryingly for her flagging rivals, she now boasts a record of winning 32 of her last 34 matches against top five players.

Furthermore, Sunday's triumph may just persuade Williams that adding to her 17 Grand Slam titles during 2014 is certainly possible, and that winning another six, to overhaul Steffi Graf, might eventually come within reach too.

But Williams declined to say whether or not 2013 was her best year.

"I live to win Slams," she said.

"I am excited to win the WTA Championships, but I would say (this season is) only top three.

"I am not going to say that this is the best. I think some years I can do better and next year, I hope -- I look forward to it."

Williams, who will turn 33 next September, did agree, however, that she might reduce the number of tournaments on her schedule in 2014 after playing more than 80 matches this year.

"I think 15 is a bare minimum....definitely not more, maybe one or two fewer, maybe 13 or 14."

Williams had needed three sets to beat Jelena Jankovic in a draining semi-final on Saturday and was in trouble on Sunday at a set down and 3-3 in the second before she reeled off nine games in succession against her 31-year-old Chinese opponent.

"I've just had a really long year, and I'm just really excited, honestly. I really didn't expect to get through this match today," admitted the American.

Asked how she had managed to refuel after her exhausting near-disaster against Jankovic, Williams said: "My mum said maybe to get out of my room and have dinner.

"I didn't do treatment and that got my mind off tennis altogether and I think it helped."

As for Li Na, Williams said she felt some empathy.

"Li is older and adding some things to her game," she said. "And I definitely want to do the same."