The incident happened in the second set of the match, when the world No. 4 received a time violation after running down the shot clock when serving at 15-30 down. Djokovic, unhappy with the call, bounced the ball away, walked up to chair umpire Mohamed Lahyani and questioned his decision. “Why do you do this man? Why do you do this man?” he asked.

However, the umpire quickly reminded him that Shanghai Masters was using an automated shot clock, which begins three seconds after the previous shot ends, leaving players with only 25 seconds to serve. Hence, the umpire has no control over delaying the start of the clock after the end of a long rally or due to crowd noise.

Following the incident, commentator Nick Lester noted that the umpire felt bad for handing Djokovic the warning. He said: “It was almost like he didn’t want to do it. He said it with a whisper didn’t he, Mohamed Lahyani there. He knew what was coming.”

Co-commentator Arvind Palmer replied: “It’s not ideal, is it? But it’s enforcing the rules. That’s half the problem, the rules aren’t always enforced. Starts automatically, goes over 25 [seconds], what are you supposed to do?”

Djokovic, however, bounced back quickly to serve an ace, before holding serve. and later fought back again later in the set when Michelsen held two set points in the deciding tie-break.

“It was the first match against Alex and I also hadn’t played in a while, so it took me a little time to get the rust off,” said Djokovic, who boasts a record 35 match wins in Shanghai. “He started off terrifically; big serves and an aggressive style of tennis… he’s not afraid to step it up and take it to his opponent.

“It was a very close encounter and I thought a high level of tennis in both sets. I’m just glad to keep calm when it mattered in the second-set tie-break.”

Djokovic, who was still donning a protective sleeve over his right knee, will next face the winner of the match between 28th-seeded Flavio Cobolli or former Grand Slam winner Stan Wawrinka.