Serena Williams beat Simona Halep 6-3, 6-0 Sunday to win her third-successive title at the WTA Finals - and her fifth overall. (Also read: Sania-Cara win WTA finals in maiden appearance)
Halep easily beat Williams just four days earlier during the group stage of the tournament, but Williams turned that around with an aggressive game plan that unsettled the Romanian player.
Williams won 11 of the last 12 games in the match to join Martina Navratilova and Steffi Graf as the only players to have won five titles in the season-ending championships.
The 33-year-old American pulled out of her previous two tournaments with illness and a knee injury, yet still claimed the $2 million first prize.
"I just started training, because I had such a bad knee in Beijing I didn't know if I'd be able to play here, and now I have won the Billie-Jean King trophy - I am so excited," Williams said.
The match was the most one-sided championship match in the WTA Finals since Kim Clijsters beat Amelie Mauresmo 6-2, 6-0 in 2003.
"It was an amazing week so I can't be too sad that I lost," Halep said. "Congratulations to Serena, you are the best."
Halep got the first break of the match in the third game and looked capable of repeating the surprise 6-0, 6-2 victory she recorded over Williams on Wednesday, but in the next game Williams broke back at her third opportunity and the course of the match was set.
Williams changed her game plan from the group-stage contest, attacking Halep's second serve with fierce ground strokes, and regularly rushed the net to cut the points short and prevent the Romanian playing her preferred style.
Williams had 25 winners against just five by her opponent.