Rafael Nadal of Spain plays a shot against David Goffin of Belgium (not in frame) during their ATP Cup tennis match in Sydney, Australia, Jan 10, 2020. (STEVE CHRISTO / AP)

SYDNEY - Spain and Serbia have progressed to the semifinals of the ATP Cup in Australia, after nail-biting matches on Friday involving the world's top two players, Rafael Nadal and Novak Djokovic.

In a tight singles match, Djokovic finally edged ahead of Canadian, Dennis Shaparvala, 4-6 6-1 7-6 (7-4), to put the Serbian team through to the next round.

The stress of the game saw Shaparvala issued with a code violation for swearing at the crowd, who became rowdy and required a reprimand from Chair Umpire Carlos Bernardes.

ALSO READ: Australia, Russia through to semifinals of ATP Cup

"This is a tennis game. The most important thing for all of us is respect," Bernardes told the crowd.

Novak Djokovic of Serbia gestures to the crowd during his ATP Cup tennis match against Denis Shapovalov of Canada in Sydney, Australia, Jan 10, 2020. (STEVE CHRISTO / AP)

"If you don't want to watch tennis, go home. Don't disturb those who are here to watch tennis."

However it was Nadal who really gave fans something to scream about. After losing his singles match against defiant Belgian David Goffin, 6-4 7-6, Nadal and his partner Pablo Carreno Busta managed an unlikely comeback against Sander Gille and Joran Vliegen, 6-7 7-5 10-7, to win the deciding doubles in a match tiebreaker against Belgium.

Rafael Nadal and Pablo Carreno Busta of Spain react to winning a point against Sander Gille and Joran Vliegen (both not in frame) of Belgium during their ATP Cup tennis match in Sydney, Australia, Jan 10, 2020. (AP Photo/Steve Christo)

The Spanish star showed why he is the world's number one, playing two incredibly stressful matches over the course of an evening and having enough composure to clinch a tiebreak.

On Saturday, Serbia will take on Russia, while Spain will face the Aussies on their home soil.

Both Australia and Russia may have been hoping to see an end to Nadal and Djokovic.

ALSO READ: Djokovic, Nadal rally for merger of ATP Cup & Davis Cup