Simona Halep saved a match point on her way to beating Bianca Andreescu and earning an opening win at the season-ending WTA Finals in Shenzhen.
The Wimbledon champion prevailed 3-6 7-6 (6) 6-3 in a first career meeting between the pair, while in another Purple Group match Elina Svitolina saw off Karolina Pliskova 7-6 (12) 6-4.
Halep was on the back-foot for much of the match against the surprise US Open winner, losing four straight games in the opening set and twice surrendering a break in the second.
Andreescu held match point on Halep's serve in the 12th game of the set but the Romanian battled back to force and win a tight tie-break, then had to come from behind again after falling a break down early in the third.
Halep said: "I'm really proud that I could fight in this way because I had a month when I didn't really practice with my back injury, but it looks like I'm still there.
"I'm really proud actually that I could fight in this way because I have a month that I didn't really practice with my back, with the injury, but it looks like I'm still there.
"Today, it was a challenge because she's 10 years younger than me. It was a good fight. I'm happy about my victory."
Andreescu is aiming to cap a magnificent season with victory in Shenzhen and admitted she would learn much from the experience of pushing Halep so close.
The Canadian said: "I think I was executing the right tactics and I didn't feel intimidated at all stepping onto the court.
"It was a good match. She fought really hard. I didn't take my chances in the second set and I am really disappointed about that."
Defending champion Svitolina was also made to fight hard before seeing off Pliskova in the opening match of the day.
Svitolina came from a break down in the opening set and saved a set point in a marathon tie-break, in which she finally took advantage of a seventh set point of her own.
Svitolina also fell a break down in the second set but battled back strongly to win four of the last five games for a straight-sets victory.
Svitolina said: "You tell yourself to stay in the moment and you just try to play one rally at a time and not rush.
"I had to be really mentally tough and try to not think so much because obviously she's a great player. I had to expect that she would step up her game."