Following the latest misdemeanour from Kyrgios, the Association of Tennis Professionals (ATP) opted to fine the 21-year-old $16,000 ($13,000/€14,000) following his on-court conduct in the shock loss.

Kyrgios, involved in a number of controversies since he burst onto the scene in 2014, criticised fans and received a code violation for swearing.

At one stage, he began walking back to his chair before a serve from Zverev, the world number 110, had landed, while he also patted the ball over the net on several occasions.

His actions have landed him in hot water with the ATP, who have fined him the maximum amount possible for breaching the "lack of best efforts" rule on the code of conduct - $10,000 (£8,200/€9,100) - while also finding him guilty for abusing a spectator and unsportsmanlike conduct.

The news overshadowed another step on the road to recovery for Djokovic, who admitted he had been struggling for motivation of late after he completed the career Grand Slam by winning the French Open in June.

The Serbian progressed in straight sets of this ATP Masters 1000 tournament with a 6-4, 6-4 win over Canada's Vasek Pospisil but was made to work hard for his place in the next round.

He is now due to up against Kyrgios’ conqueror Zverev after the German overcame Spain's Marcel Granollers 6-7, 6-4, 6-1.

World number two Andy Murray, who has set his sights on Djokovic’s place at the summit of the rankings, produced another clinical display on his way to the last eight as he beat Frenchman Lucas Pouille 6-3, 6-1.

Murray, who came into the tournament having won the China Open in Beijing at the weekend, will go up against either Gael Monfils of France or Belgium's David Goffin.

"I was able to dictate a lot of points," the double Olympic gold medallist and reigning Wimbledon champion said.

"It was a good match."

Jo-Wilfried Tsonga of France, seeded ninth, is also through thanks to a 6-7, 6-2, 7-5 success against Alexander Zverev of Germany.

Spaniard Roberto Bautista Agut awaits for Tsonga in the next round.