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ISTANBUL - Serena Williams' motivating factor in her WTA Championships triumph on Sunday was to save her own sanity, the American said after beating Maria Sharapova in the final of the season-ending tournament.

Williams capped off a memorable 2012 on the circuit with a 6-4 6-3 victory as she claimed her seventh WTA title of year.

In a near faultless performance by the 15-times Grand Slam tournament champion, Williams never faced a break point during the final and was able to produce winners every time she was put under pressure by her Russian opponent.

The 31-year-old, who also lifted singles silverware this year at Wimbledon, the US Open, the London Olympics, Madrid, Charleston and Stanford, said it was important to end the season in style if only to preserve her mental state.

"I wanted it so bad, but I didn't want to say it," Williams told reporters.

"For my own sanity I really wanted it, even though I didn't need it. I really wanted to end on a good note."

After starting the year slowly, partly due to an ankle injury sustained in Brisbane during the first week of the year, Williams has been a supreme force ending 2012 with a 58-4 win/loss record.

So often cast aside in their previous meetings, Sharapova played far better against Williams this time around but she could never get a good look at Serena's serve and that proved to be her undoing.

Williams broke Sharapova at 3-2 in the first set with a hard backhand down the line. Sharapova then fought off two break points in the seventh game with big groundstrokes but she could not get enough returns back in play to hurt the American when she was serving.

Williams then closed the first set with a kicker serve out wide that Sharapova barely got her racket on.

Never looking back, Williams again broke Sharapova to open the second with a stunning backhand crosscourt winner.

Sharapova managed to get to deuce for the first time in the eighth game of the set, but Williams responded with a forehand crosscourt winner and a service winner out wide to hold 5-3.

She then broke Sharapova to win with an outright return of serve winner.

"She had another great serving day against me - I don't think I even had a break point," said Sharapova, who has now lost 10 and won two against Williams throughout her career.

"That's one of the reasons she's such a great champion and has had a tremendous amount of success in her career."