The stunner put Sabalenka in the final against Caroline Garcia, who beat Maria Sakkari 6-3, 6-2 and has a chance to be just the second Frenchwoman to win the title at the season-ending event.
Swiatek, the French Open and U.S. Open champion and runaway leader with eight tour victories, cruised through three round-robin victories, losing just 13 games
Just like that, it was over when the 21-year-old from Poland lost the last five games against a player she had beaten in all four meetings this season.
Sabalenka didn't make it to the semifinals with the No. 1 ranking in the eight-player event last year. She was in as the seventh-ranked player, and showed how comfortable she was on the temporary indoor hard court at Dickies Arena.
I just want to make sure that every time she plays against me, she knows that she really has to work hard to get a win,” Sabalenka said.
“Only because of this thinking, I was able to play at this amazing level tonight.”
Swiatek fell behind one break in the final set with two wide forehands before another one put her down two breaks.