Jannik Sinner beat world number one Novak Djokovic twice in one day to send Italy into the Davis Cup final with a 2-1 win over Serbia on Saturday in Malaga.
Italy, who won the trophy for the first and only time in 1976, will face 28-time winners Australia on Sunday.
Sinner, who has now triumphed three times in four clashes across 11 days against Djokovic, crucially kept Italy in the tie by beating the 24-time Grand Slam winner 6-2, 2-6, 7-5 in the second singles rubber.
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World number four Sinner saved three match points as he faced Djokovic in the singles, with the 36-year-old arriving in stellar form.
Djokovic, who has won seven titles this year including three Grand Slams, was aiming to send 2010 champions Serbia into the final for the first time in a decade.
However Sinner claimed arguably the biggest win of his career, becoming the first man to beat Djokovic in a singles match at the Davis Cup since Argentina's Juan Martin del Potro in 2011, ending a 21-match streak.
"Congratulations to Italy for qualifying for (the) finals," said Djokovic.
"They deserved it, they played really well, particularly Jannik, in singles against me and then doubles, as well.
"He barely missed the ball the entire match -- so you can only say congrats and hats down for the performance like that."
Sinner won the first of their four recent battles in the ATP Finals group stage, but although Djokovic took the second to bag the title, Sinner delivered twice more in front of a full house at the Martin Carpena arena.
After easing past Cameron Norrie on Thursday, Djokovic created headlines by rowing with noisy British fans and then showing his fury at being asked to take a doping control test before that match.
The Serb was this time unimpressed by rowdy Italian fans in the doubles defeat as he ended a glittering year without the team title he craved.
Sinner, 14 years the younger at 22, broke Djokovic in the third and fifth games, racing into a 5-1 lead.
The Italian finished his superb first set with an ace, hitting 12 winners to the subdued Djokovic's one, in only 38 minutes.
With the match seemingly under control he let it slip, double-faulting on the first break point he conceded to fall 3-1 behind.
Djokovic ruthlessly capitalised, sealing the set with another break when Sinner whipped a forehand wide.
The Serbian had the momentum.
Djokovic was on top in the third set with Sinner saving two break points and unable to pressure the Serb's serve.
Sinner appeared to crack in the 10th game, giving up three match points, but then won five consecutive points to hold for 5-5. He then broke Djokovic and held comfortably to triumph.
"For me personally it's a huge disappointment, because I take the responsibility, obviously having three match points, being so close to win it," added Djokovic.
Italy took the first set of the doubles by breaking Djokovic's serve in the sixth game, as the Serbian duo struggled for a connection.
Both sides exchanged breaks in the second set, with Italy struggling through four Serbia break points to hold for 3-3.
Djokovic responded to crowd noise from Italy fans between the points, sarcastically encouraging them to make more, before waving his hands like a conductor.
It was Italy who were on song though and Sonego put them a break up for 4-3 with a smash, Serbia's bid ending when Djokovic pushed a Sinner serve into the net.
In the first singles rubber Kecmanovic lost a nail-biting first set to Musetti but responded brilliantly.
He swept to victory with a powerful forehand winner, falling to the floor in delight, although by the end of a long day, he was left with the opposite feeling.
Filippo Volandri's side return to the final 25 years after their last appearance, facing Lleyton Hewitt's Australia, who ended Finland's fairytale run on Friday.
