Unseeded Sloane Stephens held her nerve after a disastrous second set to beat Venus Williams and reach her first Grand Slam final at the US Open.
Stephens, ranked 83rd after recently returning from injury, won 6-1 0-6 7-5 in the first semi-final.
The 24-year-old is only the fourth unseeded woman to reach the US Open final in the Open era.
An all-American final is guaranteed as Madison Keys faces Coco Vandeweghe in the second semi-final.