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.

Dubai named long-term opening host of new beach volleyball championship
UAE secure AFC U23 Asian Cup quarter-final spot
Ofner's premature celebration costs him Australian Open spot in epic collapse
Semenyo on target again as Man City beat Newcastle in League Cup semi-final
Runners can set world records at Dubai Marathon under new partnership