Perhaps it was meant to end this way: Rafael Nadal and his old rival Novak Djokovic defying insurrectionists and the ages, and now hurled together for the 55th time to decide the winner of a new team tournament still trying to pull its pants on.

Anyone who might have said something about the end of an era better have ear plugs on for a while yet. Sunday’s final of the ATP Cup at Sydney’s Olympic Park promises to be the rowdiest conclusion to the new 24-nation tournament, played out by familiar faces. The fact Nadal and Djokovic are there for Spain and Serbia, respectively, makes it special.

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The two best players in the world have not met in this new tournament, which began 10 days ago and has gathered momentum from a low base of public recognition. But now Nadal, the world No 1, and Djokovic, just behind him, must assert themselves when Spain play Serbia in a packed house at the Ken Rosewall Arena.

When Nadal beat the energetic Australian Alex de Minaur, 4-6, 7-5, 6-1, in the concluding singles of the second semi-final, it was a tough blow for the young Australian, but he took it well. “I know I’ve got this level,” he said at the end of a campaign in which he came back from a set and a break twice and saved eight match points against Great Britain. “I’m showing it. It’s time for me to get in that mindset more often, where I’m believing that I can take it to anyone.

“In that match, that’s how I felt. I was playing my game and I was doing it my way. Didn’t matter what was happening. I was going to commit to my game plan and keep going for my shots and keep backing myself.

“That’s honestly the head space I’ve got to be in. That’s what I’ve got to bring to the table more often. But it’s good to know that I’ve got that extra gear, when I need to be a bit more aggressive so I can bring it out.”

Nick Kyrgios, though, was despondent after Roberto Bautista Agut beat him 6-1, 6-4. “Honestly, I hadn’t felt like that in a while, getting beat down like that,” he said. “I didn’t have my best serving night at all. I thought he played really, really well.”

Earlier, Serbia’s Dusan Lajovic played some lights-out tennis to see off Russia’s Karen Khachanov, whose challenged ebbed and flowed. But everyone was aware what the crunch match would be. There has been no shortage of excitement in this tournament, and Djokovic-Medvedev was well worth its place alongside Kyrgios-Tsitsipas, De Minaur-Evans as well as the Great Britain-Australia doubles and a few others.

Facebook Twitter Pinterest Novak Djokovic after his ‘exciting, exhausting, joyful, dreadful’ win over Daniil Medvedev. Photograph: Dan Himbrechts/AAP

However, any notion that these elite players are risking burnout so close to the start of the Australian Open on 20 January by their commitment here is a misreading of what makes them special. They have gears but, if threatened by defeat, they find another one not always available to lesser players.

Without the magic component, Djokovic could not have survived the most intense examination of his career by Nadal, Roger Federer, Andy Murray and anyone else who stretched him finals. On Saturday he came close to boiling over.

In the opening match, Lajovic beat Khachanov 7-5, 7-6 (1), feeding off the frenzy generated by a 10,000 crowd with a loud Serbian component. Dule, as the world No 34 is known, hit 26 winners and 16 unforced errors in an hour and 49 minutes, and has won four of his five matches in the tournament.

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It was a performance to set the mood for the day. Daniil Medvedev was the player most suspected would blow his top in the second, pivotal tie, but he held his nerve. The result swung, in the end, on the extraordinary game that brought the fight to a finish after two hours and 47 minutes, a see-sawing exchange in which Djokovic saved three break points and needed two match points to crush his determined foe, 6-1, 5-7, 6-4, and stop the world No 5 from completing a hat-trick of wins against him.

“Exciting, exhausting, joyful, dreadful all at once,” Djokovic said. “At one point we both refused to miss from the baseline. There were a lot of rallies and it was very exhausting. Very physical battle, but also mental battle. That was definitely one of the most exciting matches I have played against him – or any other top player – in the past few years.”

Medvedev won most of the longer rallies, as Djokovic went looking for the quick kill, a sure sign he is feeling the strain. But he has to lift himself one more time in Sunday’s final.