Elena Rybakina is on the cusp of becoming the first player to be eliminated from the WTA Finals after she fell to a three-set defeat by Zheng Qinwen in the group stages.
China's Olympic champion Zheng - playing at the season-ending tournament for the first time - won 7-6 (7-4) 3-6 6-1 in Riyadh, Saudi Arabia, for her first victory over the Kazakh in three attempts.
"I'm really happy to win this match," said Zheng, 22. "I've never beaten her before and she's one of the greatest players right now."
Should Aryna Sabalenka beat Jasmine Paolini later on Monday, fifth seed Rybakina will be eliminated having lost both of her matches at the Finals so far.