(CNN) -- Maria Sharapova kept alive her hopes of finishing the year as world No. 1 when beating Italy's Sara Errani 6-3 6-2 in her opening match of the WTA Tour Championships in Istanbul. The Russian, who won the event in 2004, has called attaining the status her 'biggest priority this week' at the season-ending tournament. The 25-year-old needs to win at least two matches in Istanbul while hoping that Victoria Azarenka, the Belarusian who currently holds the title of the world's best, slips up in the Red Group if she is to finish the year on top. Sharapova, whose victory margin was identical to her only previous meeting with Errani, who she beat in the final of this year's French Open, was delighted to make an impact at the WTA Championships after injury forced her early withdrawal last year.
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Maria Sharapova beat Italy's Sara Errani in straight sets to win opening match in White Group
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Defending champion Petra Kvitova makes 41 unforced errors as she is beaten by Agnieszka Radwanska for first time
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Serena Williams returns to action for first time since U.S. Open win, beating Germany's Angelique Kerber
The only Red Group game of the day found @placeholder playing her first match since winning the U.S. Open in August and she maintained her winning run as she beat Angelique Kerber, the German making her debut at the event for the world's top eight players.