Thanasi Kokkinakis didn’t think he was ready when he was asked to step up for Australia two years ago in the Davis Cup finals.

But this time he was and the now 28-year-old, who captain Lleyton Hewitt said would be “dangerous for anybody” after the shock decision to pick him ahead of Alexei Popyrin for the opening singles clash against the USA, delivered.

Kokkinakis defended four match points and a endured a marathon third-set tie-breaker before taking down Ben Shelton 6-1, 4-6, 7-6 (16/14) with a gripping tie-break triumph.

World No.4 Taylor Fritz then pulled the US level by beating Alex de Minaur 6-3, 6-4 in the second singles rubber before Matt Ebden and Jordan Thompson scored a 6-4, 6-4 win over Ben Shelton and Tommy Paul to secure the epic win and passage to the semi-finals.

Hewitt said he had “full belief” in picking Kokkinakis over Popyrin and he “played like the winner of the NSW Open Challenger about a month ago”.

“Me and the rest of the team know what Thanasi’s level is like, and if we can get him going out there and playing at his highest level, he’s dangerous for anybody. I don’t care who it is,” Hewitt said.

“You know, I had full belief in him. I know the rest of the boys did to go out there today. He was hitting it a treat all week leading in. He got what he deserved. He put a very tough training block in for us to get that win today, which was bloody important.”

For Kokkinakis, the win was “massive” and reaffirmed in his mind that after a horror run of injuries his capacity to tackle the world’s best was growing and he was starting to overcome doubts in his own ability.

“It’s massive. Massive for me, for the team,” he said.

“I played two years ago when we made the final, but I wasn’t ready. I had a sinus surgery sort of a few weeks before that, so this is the first time I feel like I have been able to be healthy and at least give the team a chance and put my best food forward. Happy that Lleyton had faith in me again to put me in.

“I think it’s been pretty well documented sort of the troubles I have had throughout my career. I’m 28 now, but I feel like I’ve seen a lot. I came onto the scene young. I still feel like there is a lot of good tennis in me left. I feel like I can cause an upset and play big matches and have big wins, as I have shown this year.

“So for me it’s just about trying to be consistent and playing more events. I’ve always struggled with that. Doing it for the country always seems to bring out a different sort of intensity and effort.”

The final set tie-breaker was the longest of Kokkinakis’ career and the world No.77 fell to the floor after finally converting match point.

“I have had a lot of emotional matches. Some for good; some for bad,” he said.

“But to win a match like that for Australia is huge in the finals.

“I know what I can do when I’m locked in and playing well, I thought I was practising really well all week. Maybe they believed in me there. A lot of times they believe in me more than I do myself. “

Australia will next play either nemesis Italy or Argentina in the semi-finals.