SHENZHEN, China -- Simona Halep saved a match point before beating Canadian teen Bianca Andreescu 3-6, 7-6 (6), 6-3 Monday at the WTA Finals.
Halep, a former No. 1 who won the Wimbledon title in July, saved the match point in the 12th game of the second set.
After the tiebreaker, both players sought medical treatment. Halep had her foot treated while the 19-year-old Andreescu, the US Open champion, had a lower back problem. Andreescu also called for the trainer in the third set.
Earlier, defending champion Elina Svitolina stretched her unbeaten run at the season-ending tournament into a new year, beating Karolina Pliskova 7-6 (12), 6-4 in her opening match.
Svitolina, the only player in this year's field who has not won a title this season, was unbeaten in the tournament last year.
After exchanging service breaks in the first set, Svitolina converted her seventh set point. Pliskova also had a chance to take the first set, but she failed to take advantage of a set point at 9-8 in the tiebreaker.
"You tell yourself to stay in the moment," Svitolina said of the lengthy tiebreaker. "You just try to play one rally at a time, to don't rush. Even when I had the chances to finish the set, because there was few, I thought I could play better."
After the tiebreaker, Pliskova struggled to stay in the match.
"I think that decided all match," the Czech player said. "Even though I had some chances in the second set, too, it was a big part of the match, the first set.
"Everything what I just won was because I made a winner or because I was pushing her. Overall I think she didn't give me many mistakes."
Svitolina jumped ahead 2-0 in the second set and then broke again for a 4-3 lead.
Pliskova, who had won all three of her previous opening matches at the WTA Finals, leads the tour with four titles this season -- winning in Brisbane, Rome, Eastbourne and Zhengzhou. She also leads the tour with most aces served at 481.
Halep and Svitolina are now 1-0 in the Purple Group, while Andreescu and Pliskova are 0-1.