Simona Halep saved a match point before defeating Canadian teen Bianca Andreescu 3-6, 7-6, 6-3 at the WTA Finals in Shenzhen.
Both players sought medical treatment during the match, with Halep getting her foot treated while Andreescu had a lower back problem.
Elsewhere, defending champion Elina Svitolina stretched her unbeaten run at the season-ending tournament with a 7-6, 6-4 win over Karolina Pliskova.
Halep and Svitolina are now 1-0 in the Purple Group, while Andreescu and Pliskova are 0-1.

Sulaiman Abdulrahman wins UAE's first medal at Asian Games
De Minaur stuns Zverev as Team World take 5-3 lead in Laver Cup
Russell fends off Verstappen to win in Baku, Antonelli fifth
Ireland to fulfil Nations League fixture with Israel after player vote
Kohli says 2027 World Cup will be his last for India
