Coco Gauff continued her stellar end to the season with victory over world number one Aryna Sabalenka to set up a WTA Finals showpiece against Zheng Qinwen.
American Gauff had already notched a rare win over Iga Swiatek in the group stage and capitalised on an increasingly wayward performance from Sabalenka.
Gauff beat the Australia and US Open champion 7-6 (7-4) 6-3 to reach the final of the season-ending tournament for the first time.
The 20-year-old has lost just two of her 14 matches since her US Open title defence ended in the quarter-finals in September.
She will face another first-time finalist in Olympic champion Zheng, who beat Wimbledon winner Barbora Krejcikova 6-3 7-5.
"She's playing great. Playing confident tennis will help me and give me the best shot at winning," Gauff said.
"Year-end, I consider it as a plus, and even being here is a reward for the season I've had."
This year's tournament has record prize money of £12m.
