Serena tops Azarenka at WTA Championships

In a rematch of last month's U.S. Open final, Serena Williams once again beat Victoria Azarenka, this time at the season-ending WTA Championships in Istanbul.

The third-seeded former world No. 1 Williams defeated the top-ranked Azarenka 6-4, 6-4 in 1 hour, 35 minutes indoors at Sinan Erdem Dome. The American star swatted 11 aces, compared to zero for her Belarusian counterpart, who piled up nine double faults en route to defeat.

After Williams snuck out a first-set win, Azarenka jumped out to a 3-0 second- set lead with the help of a pair of breaks. But the powerful American would not be denied on Day 3, as she roared back to win six of the next seven games and go 3-0 in this week's round-robin Red Group.

Williams captured the Red Group and had already secured a berth in Saturday's semifinals. The sizzling-hot star has now won 46 of her last 48 matches overall and is a perfect 12-0 against top-five women this season.

"Maybe I'm doing the right things at the right time," Williams said.

The 31-year-old improved to 5-0 against Azarenka in 2012, as Williams also beat the Belarusian in last month's U.S. Open finale and is now a lopsided 11-1 lifetime against Azarenka.

The 2012 Wimbledon, U.S. Open and Olympic champion Williams captured WTA Championships titles in 2001 and 2009 and is a two-time runner-up at this prestigious event.

The 23-year-old Azarenka now needs to beat Li Na on Friday to guarantee herself the year-end No. 1 ranking. If Azarenka loses, Maria Sharapova would finish the year at No. 1 if she can go 5-0 this week.

The Australian Open champion Azarenka was last year's WTA Championships runner-up to Czech left-hander Petra Kvitova.

In Thursday's opening match, the former French Open champion Li kept her semifinal hopes alive by dousing German southpaw Angelique Kerber.

The eighth-seeded Chinese star improved to 1-1 this week with a 6-4, 6-3 handling of the fifth-seeded Kerber, who went a disappointing 0-3 in her round-robin assignments.

Also on Day 3, the nightcap saw seventh-seeded Italian Sara Errani hold off ninth-seeded Aussie Samantha Stosur 6-3, 2-6, 6-0. Stosur replaced the 2011 WTA Championships titlist Kvitova in the eight-woman field on Wednesday.

Errani can reach the semis with a victory against fourth seed Agnieszka Radwanska on Friday, while Stosur's week will come to an end on Friday, win or lose, when she faces second-seeded Maria Sharapova.

The four-player Red Group here features Azarenka (1-1), Williams, Kerber and Li, while the White Group boasts the 2004 champion and 2007 WTA Championships runner-up Sharapova (2-0), the Wimbledon runner-up Radwanska (1-1), the French Open runner-up Errani (1-1) and the replacement Stosur (0-1).

The top-two players in each group advance to the semifinals, with the winners squaring off in the lucrative finale on Sunday. Sharapova, like Williams, has already secured a berth in the final four.

The winner of this $4.9 million event could collect as much as $1.75 million.