ISTANBUL - Serena Williams extended her dominance over the top-ranked player in the world on Thursday, defeating Victoria Azarenka 6-4, 6-4 at the WTA Championships.
Williams now has an 11-1 career record over Azarenka, and has won the last nine matches between the two.
Williams' win also prevented Azarenka from making sure early she would finish the year as No. 1, although the Belorussian can secure that position with another victory in the round-robin portion of the tournament.
Williams, who is projected to finish the year at No. 3 no matter what, got her third win in three matches at the event when Azarenka served a double-fault. Azarenka also lost the first set on a double-fault and finished with nine.
Azarenka squandered a 3-0 lead in the second set as Williams won the next four games to battle back.
Li Na beat Angelique Kerber of Germany 6-4, 6-3 in another Red Group to retain a slim chance of advancing.
Li's first win in two round-robin matches means the Chinese can still reach the semifinals, depending on other results in her Red Group.
The fifth-ranked Kerber, making her first appearance in the season finale, bowed out losing all three of her matches but played some outstanding tennis at times. She played more than three hours late Wednesday in a three-set loss to Azarenka.
The tournament brings together the top eight players in the world. They are split into two groups and two from each advance to the semifinals.
Williams and Maria Sharapova, who was idle Thursday, have already qualified for the last four.
Sharapova, the French Open champion, could still take the No. 1 ranking away from Azarenka.
Williams has dominated the second part of the season, winning Wimbledon and the U.S. Open and also capturing th Olympic gold medal. She has won 46 of her last 48 matches.