Novak Djokovic fired Serbia into the final of the ATP Cup in Sydney after defeating Russia's Daniil Medvedev.

Djokovic took the opening set before word number five Medvedev bounced back to take the second.

But Djokovic showed his class in the deciding rubber to take a 6-1 5-7 6-4 victory, and book a showdown against Spain or Australia in Sunday's showpiece.

It sealed an unassailable 2-0 lead for Serbia after Djokovic's team-mate Dusan Lajovic defeated Karen Khachanov 7-5 7-6 (1).

"It was exciting, exhausting, joyful, dreadful all at once," said Djokovic on the tournament's website. "At one point we both refused to miss from the baseline, so it was a lot of rallies and it was very exhausting.

"It was a very physical battle, but also a mental battle, too. Definitely one of the most exciting matches I have played against him or any other top player in the last few years."

In the doubles, Nikola Cacic and Viktor Troicki completed a 3-0 whitewash for Serbia after they saw off Teymuraz Gabashvili and Konstantin Kravchuk 6-4 7-6 (7).