Roger Federer (pictured) will face great rival Novak Djokovic at the Australian Open semi-finals on Thursday. — Photo tenniswordusa.org

MELBOURNE — Roger Federer faces great rival Novak Djokovic for a 50th time while home hope Ashleigh Barty will have the nation urging her on in the Australian Open semi-finals on Thursday.

Swiss maestro Federer finds himself in the unfamiliar position of underdog when he takes on the reigning champion in Melbourne, where temperatures are set to soar to 37 degrees Celsius.

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

The 38-year-old 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.

But Djokovic says that 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, between Alexander Zverev and Dominic Thiem, is on Friday.

In the women's semi-finals, Australia's world number one and top seed Barty will be strong favourite against 14th-seeded American Sofia Kenin.

They have met five times before, with the 23-year-old Barty winning four of them.

Kenin, 21, contesting her first Grand Slam semi-final, will have to deal with a ferociously pro-Barty crowd at the 15,000-capacity Rod Laver Arena.

"I'm excited, my team's excited," said Barty, the French Open champion who is attempting to win her home Grand Slam for the first time.

"We love the opportunity of getting another match out on that beautiful court."

The other women's semi-final, also Thursday, is between two former world number ones in Simona Halep and unseeded Garbine Muguruza.

They have each won Wimbledon and Roland Garros, but never the Australian Open. — AFP