Melbourne, Jan 30 (AFP) Unheralded American Sofia Kenin stunned world number one Ashleigh Barty to end home hopes at the Australian Open on Thursday, as Roger Federer and Novak Djokovic prepared for the 50th instalment of their great tennis rivalry in a blockbuster semi-final.

Barty had sent Australian expectations soaring of a first home-grown winner since 1978, but they came crashing to earth against the aggressive 14th seed, who saved two set points in each set to win 7-6 (8/6), 7-5.

Moscow-born Kenin, 21, looked stunned at reaching her first Grand Slam final, at a tournament where she has often gone unnoticed while fellow Americans Serena Williams and 15-year-old Coco Gauff hogged the headlines.

"I'm just speechless, I honestly can't believe this. I've dreamed about this moment since I was five years old... I've worked so hard to get here," said Kenin, who was a baby when her family moved to America with just a few hundred dollars to her name.

"She came up with some really great shots. I knew she wasn't going to give it up to me -- I really had to fight out here. There's a reason she's number one."

Kenin's win came on a day when temperatures hit 38 Celsius (100.4 Fahrenheit), prompting play to be suspended on outside courts -- following earlier problems with bushfire smoke, downpours, wind and even muddy rain at the season's opening Major.

The American will face another heavyweight in Saturday's final, with the second semi featuring Wimbledon champion Simona Halep and Garbine Muguruza, the two-time Major-winner who is back in a hot streak of form.

- 'Fighter' Federer -

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Later on Rod Laver Arena, Federer and Djokovic -- who have carved up 12 of the last 14 Australian Open titles between them -- will play for a place in the final.

Djokovic, 32, leads 38-year-old Federer 26-23 in their head-to-head, and while the Serbian has moved serenely into the last four, Federer made it by the skin of his teeth.

He was two points from defeat against John Millman in the third round and, incredibly, saved seven match points in his quarter-final against Tennys Sandgren.

A groin problem during Federer's miraculous escape against Sandgren could also hinder his chances of making it seven titles in Melbourne and stretching his record for Major wins to 21.

But Djokovic says Federer's heroics against the 100th-ranked American are exactly why the 20-time Grand Slam winner is to be feared.

"What he did was amazing, he showed me he's one of the best players of all time," said Djokovic, who is targeting a record eighth title in Melbourne.

"I mean, he never gives up. When it matters the most, he's focused and he plays his best tennis. He's a great fighter."

The other semi-final, on Friday, is between Dominic Thiem -- who shocked world number one Rafael Nadal -- and Alexander Zverev, the long-admired German talent who is into a Grand Slam last four for the first time. (AFP)

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