America's Sofia Kenin stunned a nervous-looking Ashleigh Barty to win their semi-final clash in straight sets and reach her first Grand Slam final.

The 14th seed won 7-6 (8-6) 7-5 to end World No 1 Barty's dreams of becoming the first Australian woman to reach the final at the slam in 40 years.

In sweltering temperatures at Melbourne Park, the 21-year-old American remained ice cool while top seed Barty showed signs the pressure had got to her, missing set point chances in both sets.

She capitalised on an error-strewn first set from Barty, who hit an uncharacteristic 21, and despite trailing in the tie-break, claimed four in a row and the first set was in the bag.

Barty seemed to have shaken off some of the nerves as she came out fighting in the second and quickly took her first break of the match to go 2-1 up.

Unfazed by this, the young American remained calm and claimed her own maiden break after Barty missed a crucial service for the set at 5-4.

Kenin then showed her class as she stormed through the next two games, making it three in a row and a first Grand Slam final.

“I believed I could win even though I had two set points down in the first and second,” she said afterwards.

“I could literally feel, I was telling myself, I believe in myself. If I lose the set, I'm still going to come out and believe. Yeah, I really did a great job with it. I didn't give up."

She will now face Spain's Garbine Muguruza, who shocked Wimbledon champion, Simone Halep in straight sets 7-6(8) 7-5.