Italy will face Australia after they earlier defeated record 32-time winners the US and world number four Taylor Fritz with a tense 2-1 victory.
Sinner won his first two Grand Slams this season, as well as triumphing at the ATP Finals last week without dropping a set, and blew Sebastian Baez away 6-2, 6-1 after Francisco Cerundolo comfortably beat Lorenzo Musetti 6-4, 6-1 in the opening rubber.
In the decisive doubles battle, Sinner and Matteo Berrettini shaded Andres Molteni and Maximo Gonzalez 6-4, 7-5 to progress.
“If they put me on the court in doubles I try my best,” said Sinner.
“Matteo played unbelievable today, he carried me.”
Italy booked a third consecutive return to the semi-finals and are favourites to win the Davis Cup for a second year running, in no small part because of Sinner’s presence.
The 23-year-old is still waiting for the outcome of the World Anti-Doping Agency’s appeal against his initial exoneration for twice testing positive for traces of the steroid clostebol in March.
Sinner beat Novak Djokovic in singles and doubles in last year’s semi-finals on the way to helping Italy end a 47-year wait to lift the trophy again.
Against Baez in the first set of his singles match, the Italian spurned five chances to close it out but eventually did so at the sixth time of asking.
Sinner broke in the second and fourth games of the second set, before holding on to serve out the match.
The doubles teams were tied until the ninth game of the first set when Sinner won three points and then Molteni clipped his passing shot which was heading wide to hand Italy the decisive solitary break.
The second set was even tighter with Italy breaking for a 6-5 lead and sealing their victory with a Sinner smash.
“It’s a different feeling when you step on court and can enjoy playing with the best player in the world,” said Berrettini.
Green and gold triumphant
Australia’s match-up with the USA was the most played in Davis Cup history with this their 48th meeting – the first was in 1905.
In the opening rubber, Australia’s Thanasi Kokkinakis edged Ben Shelton 6-1, 4-6, 7-6 (16/14) with a gripping tie-break triumph.
Fritz pulled the US level in the tie by beating Alex de Minaur 6-3, 6-4 before Matthew Ebden and Jordan Thompson scored a 6-4, 6-4 win over Shelton and Tommy Paul.
Australia, who have lifted the trophy 28 times, second only to the USA, last won the tournament in 2003 and finished as runners-up in the last two editions.
With Fritz leading the charge for a strong US squad, the Americans were hoping for a first title since 2007.
However, Kokkinakis’ tie-break heroics and Australia’s doubles team won them an even quarter-final clash.
“We had to rush out here and get the job done for our country and we love nothing more than those pressure moments,” said veteran Ebden, 36.
World number 77 Kokkinakis saved four match points and spurned six of his own before eventually prevailing to end the thrilling tie-break, the joint-sixth longest in the competition’s history.
“I don’t know if I’ve been that pumped up in my life, I wanted that one bad, I wanted to help my team,” said the Australian.
After Fritz – who finished as runner-up in the ATP Finals last week – defeated De Minaur, US captain Bob Bryan opted for two singles players in Shelton and Paul over his doubles specialists and paid the price.
“This wasn’t a black-and-white decision, it was a razor-thin edge, you know, and we went with it,” said Bryan.
“We knew it could have turned out like it did, because we’re playing a tough team… but I don’t regret anything about this (choice).”
Australia were beaten by Italy in 2023’s final and will be out for revenge on Nov 23.
“If we’re up against them we’ll be up for the challenge – but it’s not going to be any easier than it was last year, either,” said captain Lleyton Hewitt.
The Netherlands, who defeated Rafael Nadal’s Spain on Nov 19, tackle Germany in the first semi-final on Nov 22.