Novak Djokovic of Serbia reacts to winning the first set against Daniil Medvedev of Russia (not in frame) during their ATP Cup tennis match in Sydney, Australia, Jan 11, 2020. (STEVE CHRISTO / AP)

SYDNEY - Serbia is through to the ATP Cup final after beating Russia in both singles matches here on Saturday, securing their place in the championship decider of the inaugural tournament.

The first singles match saw Dusan Lajovic beat Karen Khachanov, 7-5, 7-6 (1), setting up world No. 2 Novak Djokovic to carry his team through to the finals.

However in a thrilling off script performance, it took Djokovic three sets to defeat fifth-ranked Daniil Medvedev 6-1, 5-7, 6-4.

READ MORE: Spain, Serbia through to ATP Cup semi-finals

Daniil Medvedev of Russia plays a shot against Novak Djokovic of Serbia (not in frame) during their ATP Cup tennis match in Sydney, Australia, Jan.11, 2020. (STEVE CHRISTO / AP)

As the second set slipped through his fingers, a visibly frustrated and exhausted Djokovic smashed his racquet to pieces on the court's surface.

"Yesterday I spent almost three hours on the court, today was pretty similar - lot's of rallies, probably more rallies than yesterday's match and it was very exhausting," Djokovic said in a post match interview.

Dusan Lajovic of Serbia makes a forehand return to Karen Khachanov of Russia (not in frame) during their ATP Cup semifinal tennis match in Sydney, Australia, Jan 11, 2020. (STEVE CHRISTO / AP)

The Serb heaped praise on his opponent who despite losing the match can hold his head high for having squeezed every inch out of the reigning master.

"Daniil Medvedev is one of the best players in the world and today he showed why. He's very difficult 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.

Serbia will meet either Spain or Australia in the final depending on who wins Saturday evening's match-up.

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