World number one Djokovic featured in both a singles and doubles rubber on the Rod Laver Arena. 

He first defeated Denis Shapovalov 7-5 7-5, before joining Filip Krajinović to beat Milos Raonic and Shapovalov 7-5 7-6. 

Raonic then overcame Dušan Lajović 6-3 6-4 to prevent a Serbian clean sweep. 

"Filip Krajinovic was the key," said Djokovic. 

"The way he played today is phenomenal."

Russia now top Group D after a 2-1 triumph over Argentina on the Melbourne Arena. 

World number four Daniil Medvedev overcame world number nine Diego Schwartzman 7-5 6-3, while Andrey Rublev eased past Guido Pella 6-1 6-2. 

Argentina earned a consolation point after Maximo Gonzalez and Horacio Zeballos secured a 6-4 7-6 win against Rublev and Aslan Karatsev in the doubles rubber. 

"I'm really happy with the win of the team, because it's not an individual competition," said Medvedev. 

"I have some things that I can improve, but it's the first match after two months without competition, which is never the same as practice. 

"So I'm happy with the win."

Roberto Bautista Agut temporarily became Spain's number one singles player after Rafael Nadal announced he would miss the tie with a stiff back. 

Bautista Agut came back from a set down to win 4-6 6-4 6-4 against Alex de Minaur of Australia. 

Pablo Carreno Busta then got past John Millman 6-2 6-4, before joining forces with Marcel Granollers to overcome John Peers and Luke Saville 6-4 7-5 and secure a 3-0 result over the Australian team. 

"Everybody knows that to have Rafa on the team is a pleasure," said Bautista Agut.

"It’s a privilege to be in the team with him. 

"We can learn a lot of things staying around him. 

"He has been fighting 20 years in a row and we are there to complete the team, to be there and to fight. 

"I think Pablo and I today did a great job."

Italy earned a 2-1 win over Austria, with Matteo Berrettini of Italy beating Dominic Thiem of Austria 6-2 6-4 before Austrian Dennis Novak beat Italian Fabio Fognini 6-3 6-2. 

The pair then came up against each other in the doubles rubber and Berrettini was triumphant again. 

He and Fognini comfortably defeated Thiem and Novak 6-1 6-4. 

Competition is scheduled to continue tomorrow with matches between Germany and Canada, Greece and Australia, France and Italy, and Russia and Japan.