Serena broke twice in the first set and lost just seven points on serve in her last match of the year. She looked sharper than Venus in every facet of a match that featured few long rallies and little of the spectacular tennis the two have provided in some of their previous meetings.

Serena sealed the match with a crosscourt forehand winner and celebrated with a simple fist pump before hugging her sister at the net.

"It feels great," said Serena, who also won the WTA Tour's season-ending event in 2001. "I totally didn't expect to come here and win."

Venus exhausted

After playing four late-night three-setters this week in temperatures hovering around 30 C, Venus seemed to run out of steam in the final.

Serena held five of her last seven service games at love and lost just one point in each of the other two.

"I don't think I returned as well as I wanted to," said Venus, the defending champion. "Sometimes I made her service games a bit too easy."

It was Serena's fourth straight win over her sister. She also beat Venus in the round-robin stage of the Doha tournament, the Wimbledon final and the semifinals in Miami this year. She leads their head-to-head record 13-10.

"Playing a final against Venus is really tough," Serena said. "Even though she wasn't really feeling great, she kept hitting every ball back."

It was Serena's third tournament win of the season after taking the Wimbledon and Australian Open titles.

"I haven't won a tournament that wasn't a Grand Slam in a while, so that was even more exciting," she said. "My losing streak in (other) tournaments is over."

Serena pocketed US$1.55 million for the win after finishing the event undefeated - bringing her total prize money for the year to a record US$6.19 million. Justine Henin held the previous record of US$5.43 million in 2007.

She also clinched the year-end No. 1 ranking earlier this week after Dinara Safina of Russia pulled out injured in her first match.

The tournament features the eight top-ranked women in the world divided into two groups, with the semifinalists decided by a round-robin stage.

Venus lost two of her three round-robin matches but still advanced. She then rallied for a three-set win over Jelena Jankovic on Saturday but looked sluggish from the start in the final.

"It was the end of the season, so I have no complaints," Venus said about her fitness level. "You have to show up and play no matter what. So that had nothing to do with it."

Venus played with her left knee strapped while Serena had strapping on her left thigh.

"We definitely weren't physically 100 percent out there today," said Serena, a day after pulling out of next weekend's Fed Cup final against Italy. "Right now, I'm just struggling in every aspect of my body."