In temperatures that hovered near 40 degrees Celsius (104 Fahrenheit), the 21-year-old saved set points in both sets to defeat the world No. 1, 7-6 (6), 7-5 in one hour, 45 minutes.
It ended Barty’s bid to become the first Australian woman to win in Melbourne since Chris O’Neil in 1978. The “Barty Party” — a term that trended around the world during Barty’s 2019 run — came to an abrupt halt.
Kenin, meanwhile, became the first US woman other than Serena or Venus Williams to make the Australian Open final since Lindsay Davenport in 2005.
Kenin — who ousted crowd favorite Coco Gauff in the fourth round — idolized Maria Sharapova growing up.
Like Sharapova, she was born in Russia before moving to Florida at a young age.
She made great strides last season, beating Serena Williams at the French Open and fellow grand slam champions Bianca Andreescu, Naomi Osaka and Barty.
Kenin will face either Simona Halep or Garbine Muguruza in Saturday’s final.
Both are two-time grand slam winners, titling at the French Open and Wimbledon.
Thursday’s opening semifinal was played entirely outside, though it came close to being suspended due to the heat. It would have been postponed if the tournament’s heat scale reading hit five. It reached as high as 4.9.