Elina Svitolina claimed the fourth and final WTA Elite Trophy semi-final berth on Friday when she fought back from a set down to beat Carla Suárez Navarro.
Svitolina, who also beat Andrea Petkovic in her first game, finished at the summit of Group B to join Venus Williams, Karolina Pliskova and Roberta Vinci in the semis.
Her battle against Suárez Navarro on Friday lasted just over 160 minutes, with the marathon first set taking up 81 of those and the final score reading 6-7(4-7), 6-1, 6-3.
"It was such a crazy match today. I was playing really well out there, and Carla was playing really well as well,” Svitolina told the WTA website.
“It was a marathon match and really tough obviously, but I was really happy with how I played today. This is a big win.
"It was amazing support today. It's really an amazing feeling when fans like this are watching and supporting you."
Svitolina will face Pliskova in the semis, after the latter won both of her games against Jelena Jankovic and Sara Errani.
Meanwhile, in the other group stage matches played on Friday, Vinci suffered a 6-1, 6-0 defeat to Anna Karolina Schmiedlova and Madison Keys lost 6-3, 6-2 to Saisai Zheng.
Vinci won just one of the two matches she played, but qualified based on her higher number of set victories after Caroline Wozniacki retired from her game against Svetlana Kuznetsova and pulled out of the tournament before her scheduled match against Vinci on Friday.
The Italian will meet Williams in the semis after the American won both of her games against Keys and Zheng.
"Winning here would be a great way to end the year. But I think that's what everyone who's still in contention is hoping for. I'm not going to be the only one,” Williams said.