Dominic Thiem will meet defending champion Novak Djokovic in Sunday's Australian Open final after digging deep to beat Alexander Zverev.
Thiem, 26, won 3-6 6-4 7-6 (7-3) 7-6 (7-4) in a match briefly interrupted by rain and a lighting failure.
The Austrian fifth seed said "it was an unreal match" and he will now look to win his first Grand Slam, after losing the past two French Open finals.
Djokovic is favourite to win a record-extending eighth title and 17th major.
The 32-year-old has lost just three matches in the past 10 Australian Open tournaments.
German seventh seed Zverev, 22, was bidding to reach his first Grand Slam final but instead, it his good friend who will play for the title.
"To reach the Australian Open final is unreal," said Thiem, who will bid to become only the second Austrian player - after Thomas Muster at the 1995 French Open - to win a Grand Slam.
"Two tie-breaks, so tough and so close, it was almost impossible to break him."
Third time lucky for Thiem?
Thiem produced a heroic effort, physically and mentally, to beat Spanish top seed Rafael Nadal in an epic quarter-final that lasted more than four hours on Wednesday.
As a result it looked as though the Austrian, who said he did not get to sleep until 5am following that win, was lacking energy against Zverev.
The crushing groundstrokes he produced against Nadal initially lacked fizz, largely down to being pinned back by the big-serving German.
"It is not easy because I played four hours and 10 minutes against Rafa, who is the most intense man on tour," said Thiem, who is through to his first Australian Open final.
"I had some troubles in the first set, it was both of our first semi-finals here and it was not easy."
But Thiem fought back in the second set, hitting cleaner and helped by a horror of a service game from the German, to level.
The unforced error count crept up again in the third, seemingly as a sign of fatigue, but he recovered when it mattered most.
After saving two set points at 5-4 in the third, Thiem started the tie-break with a deft pick-up at the net which provided the momentum - following that with an ace, two service winners and pair of blistering winners off either wing - to clinch the lead.
That was the fourth tie-break he had won in a row, following the three which saw him beat Nadal.
It also provided the confidence that took him through the fourth-set decider.
After two loose errors led to him being pegged back, Thiem was helped when Zverev whacked an overhead wide of the doubles court for a 4-2 lead.
The tension and drama increased when the umpire overruled a call that Zverev hit long at 4-3. The point was replayed with Thiem landing a ferocious forehand to win it.
Another winner brought up three match points for the Austrian and he took the second when he sprung forward to put away a forehand volley at the net.
Thiem broke out into a beaming smile before sharing a warm hug with his opponent, whom he has known since their junior days.
"In all of the tie-breaks I think I was 2-0, 3-0 up and it gives you confidence for the rest," he said.
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