Coco Gauff confirmed her semi-final spot at the WTA Finals with a rare win over defending champion Iga Swiatek.
The American beat second seed Swiatek 6-3 6-4 to join Aryna Sabalenka in the last four in Riyadh, Saudi Arabia.
The result also means Sabalenka will be the year-end world number one as number two Swiatek can no longer catch her in the rankings.
It is only the second time Gauff has defeated Poland's Swiatek in 13 attempts.
"It feels great," said 20-year-old Gauff. "I knew going into the match, despite our head-to-head, I had a lot of confidence and I felt like I was playing great tennis.
"Even when I was playing a little bit sloppy, the games that I lost were still going to deuce. That gave me confidence and I knew if I stayed solid I had the chance to close out the match."
Earlier, Gauff’s compatriot Jessica Pegula became the second player to be eliminated from the season-ending tournament - after Elena Rybakina on Monday - following her 6-3 6-3 defeat by Barbora Krejcikova.
Swiatek must beat Pegula in Thursday's final Orange Group match to progress, while Gauff has to hold off Czech Krejcikova in order to top the group standings.