Djokovic's head-turning 6-1 5-7 6-4 victory over Daniil Medvedev added to Serbia's earlier singles result to book their place in the competition's final showdown. A very physical battle, but also a mental battle.
Earlier, Dusan Lajovic won 7-5 7-6 against Karen Khachanov, and Serbia also scored a double-double as Nikola Kacic and Viktor Troitsky defeated Teimuraz Gabashvili and Konstantin Kravchuk.
Novak ended his run in the round robin after defeating Daniil Medvedev 6-1 5-7 6-4.
As the second set slipped through his fingers, a visibly frustrated and exhausted Djokovic smashed his racquet to pieces on the court's surface.
"Paying tribute to Medvedev, Djokovic said of the match: "[It was] exciting, exhausting, joyful, terrible all at once.
Goffin had two more break points to go 5-3 up in the second, but Nadal clung on and became more offensive to take the match to a tiebreak before the Belgian closed it out for one of the biggest wins in his career. "He's very hard to break from the baseline, very tall, he's got a good serve and this was the greatest challenge I've had so far this year", Djokovic said. Djokovic, warming up for his bid to win an eighth Australian Open crown this month, went into the clash at Sydney's Ken Rosewall Arena leading their head-to-heads 28-26.
It was then up to Alex De Minaur to keep Australia alive, but he had to beat Rafael Nadal.
Nadal came dangerously close to suffering back-to-back losses for the first time in his 206 weeks as world No.1, having been shocked 6-4 7-6 in his singles loss to Belgium's David Goffin in the quarter-finals on Friday night.
In their previous two meetings - at Wimbledon in 2018 and the Australian Open a year ago - de Minaur had managed to win a total of just 14 games against Nadal, compared to the Spanish legend's flawless 36.
"He had a lot of energy, he plays with a lot of passion, sometimes a little too much", Nadal said. He improved to 5-0 at the ATP Cup with his surprisingly easy 6-1, 6-4 win against Australia's Nick Kyrgios, who came in undefeated and fully embraced the concept of being a part of a team.
The 16-time grand slam champion said he was taking a lot of energy from his matches in Sydney.
"Anyways, for me to play the match, I've got to play a very aggressive game". Novak likes to play here and Serbia has a great team and is playing very well. But Roberto played an fantastic match this afternoon and we have a good team, so we are ready for it. Nadal, on the other hand, acknowledged that Djokovic played well in the past week. "I know I have to be ready to play at my highest level to have my chance (on Sunday)". Nadal has already recently led his team to the Laver Cup and Davis Cup titles.