Top-ranked Victoria Azarenka saved two match points before rallying past Angelique Kerber of Germany 6-7 (11), 7-6 (2), 6-4 on Wednesday in her first match at the WTA Championships.
Azarenka needs just one more round-robin win to secure the No. 1 ranking for the year.
In another Red Group encounter, Serena Williams proved that even when her serve is malfunctioning, she can still beat a top player.
Williams beat 2011 French Open champion Li Na of China 7-6 (1), 6-3 for her second win in round-robin matches to close in on the semifinals at the tournament for the top eight players in the world. Maria Sharapova and Agnieszka Radwanska were scheduled to face off in the day's final match.
Williams had six double-faults and won only 51 percent of points on her first serve. But Li also struggled on serve -- there were eight breaks in the first set and three more in the second.
''My serve just didn't go in. Every time I got my first serve in, I was surprised,'' Williams said. ''But know...