Novak Djokovic battled nerves, frustration and the heat as he led Serbia’s 2-0 demolition of Canada’s pair of NextGen young guns on Friday to earn a place in the semi-finals f the ATP Cup.

The morning in Sydney stated well for Serbia, with Monte Carlo finalist Dusan Lajovic gaining the first point for his Balkan nation through a 6-4, 6-2 thrashing of Felix Auger-Aliassime.

Djokovic, who was struggling at times in the hothouse temperatures in excess of 32 Celsius, emerged with a 4-6, 6-1, 7-6(4) comeback over Denis Shapovalov.

World No. 2 Djokovic worked for nearly two and a half hours to get past Shapovalov and increase his unbeaten record against Canadians to 23-0.

His victims have included Milos Raonic (9-0) and Vasek Pospisil (5-0); he beat Shapovalov for the fifth time without a loss.

“This is one of the closest matches I’ve played against Denis,” Djokovic said.

“It was very tough, we played aggressive and served great.

“We both fought until the last shot. Serbia are through to the semis and we are sending our best regards to everyone at home.”

Shapovalov contributed 15 aces to the ongoing bushfire relief effort as he took the loss.

Djokovic came to the knockout phase in Sydney after winning all six of his singles sets in the group phase in Brisbane.

Serbian captain Nenad Zimojinovic becomes the third former No. 1 player – doubles, 2008 – to captain a side into the  inaugural edition of the Cup. he joins Lleyton Hewitt (Australia) and Russia’s Marat Safin in that specialised statistical category.

Earlier, chair umpire Carlos Bernardes was forced to halt an ATP Cup match in Sydney today between Novak Djokovic and Denis Shapovalov as partisan fans began to yell during serves and points.

Canadian Shapovalov complained of crowd noise while returning a Djokovic serve at 1-3 in the second set, and received a penalty for unsportsmanlike conduct after goading the fans.

Chair umpire Carlos Bernardes explained to the coach Shapovalov should tell him if fans become abusive and he would have them removed from the arena.

But the intense atmosphere continued through the next game, with Bernardes then having to intervene and tell off fans. “Ladies and gentlemen, please. One moment, please. This is a tennis game. The most important thing between all of us is respect,” he said.

“If you guys will do this against Canadians or Serbians, this is not what we want. Please. Respect both players. Thank you.”

While most fans applauded, others continued to jeer both players on the very next serve, frustrating Bernardes further.

“If you don’t want to watch tennis, just go home. Rather than disturb the people who are here to watch tennis,” he added.