Dominic Thiem will face Alexander Zverev for a place in the final, a match-up scarcely imaginable at the start of the tournament, after beating Rafael Nadal.
Dominic Thiem ended six years of Grand Slam frustration against Rafael Nadal on Wednesday with a seismic 7-6(3) 7-6(4) 4-6 7-6(6) upset that booked his maiden Australian Open semi-final and rocked the old guard of men's tennis.
After pulling off a nerve-shredding win that quashed doubts about his prowess on hardcourts, the 26-year-old Austrian will face Alexander Zverev for a place in the final, a match-up scarcely imaginable at the start of the tournament.
Fifth seed Thiem will head into Friday's clash against the young German, brimming with confidence, having ended top seed Nadal's bid for a record-equalling 20th Grand Slam title, despite a few wobbles on the way to victory.
Turning the tables on the man who had beaten him in all five of their previous Grand Slam meetings, including the last two French Open finals, Thiem became only the second Austrian to reach the last four at Melbourne Park, following Thomas Muster's runs in 1989 and 1997.
In a grandstand finish with the terraces roaring, Nadal saved two match points in the decisive tiebreak but surrendered on the third when he slammed a forehand into the net.
The result was different but the match had echoes of the pair's five-set marathon at the 2018 US Open quarter-finals when Nadal finally prevailed after four hours and 49 minutes of gut-wrenching play.
This time, after four hours and 10 minutes, the Spaniard left with plenty of regrets and, most likely, some ill will toward the net.
The net cord was decisively in Thiem's corner. He clipped it with a backhand winner that secured the final match point.
"I really feel I was lucky in the right situation, the net cord was really on my side," an exhausted Thiem said on court.
"It's necessary because he's one of the greatest of all time, biggest legend the sport ever had. So you need some luck to beat him."
Nadal had his chances. He failed to convert set point when serving for the opening frame and let Thiem off the hook again when 4-2 up in the second.
After wrenching the momentum from the Austrian with a brave third set rally, Nadal gave it right back, squandering three break points early in the fourth set and then promptly dropping serve.
The Mallorcan has overcome bigger problems in a long and brilliant career, so there was never any danger he would ever go quietly.
He scrapped deep into the set and the pressure finally told on Thiem, who crumbled when serving for the match at 5-4.
Thudding into the net after a double-fault, Thiem handed the break back to Nadal with a wild forehand.
"Special situation for me, serving for the match against Rafa for my first semi-finals here," said Thiem, with a laugh.
"Mentally tough situation, couldn't handle it."
But for once the indefatigable Spaniard was unable to make Thiem pay.
Even when Thiem took a tumble mid-rally during the final tiebreak, he scrambled to his feet to take a 5-2 lead when Nadal punched a backhand into the tramlines.
On the first match point, Thiem wound up his forehand for a killer blow but bashed straight into the net.
The crowd then gasped when Nadal bravely challenged a line call on the second match point after Thiem's defensive lob tested the baseline.
The technology backed Nadal but his backhand failed him on the final point, planting the ball into a net that seemed against him all night.
"Of course, I am sad. I lost an opportunity to be in the semi-finals of another Grand Slam," said Nadal.
"But I lost against a great opponent. And he deserves it, too. Well done for him."