Li Na opened her WTA Championship campaign with a 6-3, 7-6 (5) victory over Sara Errani on Wednesday.
Errani also lost her opening match on Tuesday to Victoria Azarenka and likely will be eliminated.
Li trailed 3-1 in the second set but won the next four games — and then could not close it. She twice served for the match and both times dropped her serve. Trailing 3-1 in the tiebreaker, Li won the next five points. She used her third match point when Errani sent a forehand into the net.
The tournament brings together the top eight players in the world. They play two round-robin groups, with the top two finishers in each advancing to the semifinals.