SYDNEY - The final eight places of Australia's inaugural ATP Cup are now set with Belgium and Canada sneaking through to the quarter final stage on day six action of the tournament.

With all the Group Stage matches completed late on Wednesday night, the two best-placed runner's up will now join pool winners Australia, Great Britain, Serbia, Spain, Argentina and Russia in the all-mens, 24-nation round robin tournament.

Looking in superb form since landing in Brisbane, world number two Novak Djokovic and his Serbian outfit beat out Chile 2-1 and in the following fixtures South Africa upset France 2-1 on the back of some Kevin Anderson brilliance.

In Perth, world number one Rafael Nadal's Spanish side demolished Japan 3-0, while Georgia scrapped past Uruguay 2-1.

One of the matches took a very bizarre turn when Uruguay's Pablo Cuevas was warned by the chair umpire over lack of effort.

In response, Cuevas began to jump around the court in a strange and comical way.

Threatening to leave the court and boycott the match, it was his opponent Nikoloz Basilashvili, who convinced Cuevas to stay.

"For me it was an overreacting call from the referee," Basilashvili told reporters after the match.

"I just told him it was a bad call from the referee and let's continue playing."

Basilashvili eventually won the contest 6-4, 1-6, 6-4.

In Sydney, Poland were too strong for Austria, winning 2-1, while Argentina thrashed Croatia 3-0 thanks to a stunning 7-6 (1), 6-3 upset by Guido Pella over former U.S. Open Winner Marin Cilic.

Starting Thursday in Sydney, Great Britain will take on Australia and Argentina will face down Russia.

On Friday, Serbia is set to collide with Canada, while Spain will battle it out with Belgium.