World number one Iga Swiatek is out of the season-ending WTA Finals in Texas after a shock three-set semi-final defeat by Aryna Sabalenka.
Poland's Swiatek had not dropped a set throughout the Finals but was undone by her opponent's powerful forehand.
"The only thing I had in my mind was 'just make her work'. And that's it," said 24-year-old Sabalenka.
"It's only because of that I was able to show unbelievable tennis tonight and get this win."
Victory marked Sabalenka's first win in five meetings with Swiatek this season.
She is only the third female player to beat the first, second and third seeds at a tournament since 2000 after her wins over Swiatek, Ons Jabeur and Jessica Pegula.