The incident happened after 10-time champion Djokovic, leading 6-3 4-2 at the time, saw a pacy return from world number 75 Van de Zandschulp go long for deuce.
In a split-second, Djokovic casually hooked the ball left.
“I don’t even think he knew the ball kid was there. But it was three inches from getting defaulted,” said former Wimbledon champion Pat Cash, who was analysing the third-round match for BBC Radio 5 Live.
“He’s hit that in an area where nine times out of 10 is probably a default. He’s managed somehow to sneak in between the ball kid and the spectators to the left.”
In New York little over five years ago, it was a clear-cut case.
Djokovic took a ball out of his pocket and hit it behind him, striking the female line judge in her throat.
It was an infamous incident which the Serb swiftly apologised for, saying it had left him “really sad and empty”.
Given he felt he needed to apologise again in Melbourne, many will question whether Djokovic has learned his lesson.
He also fell awkwardly during the third set and, shortly afterwards, received treatment for a blister on his right foot.
But ultimately Djokovic won in two hours and 44 minutes, keeping up his record of not yet dropping a set at this event, and a lighter workload could prove critical for his hopes of winning standalone record 25th Grand Slam singles title.
He will play Czech 16th seed Jakub Mensik in round four.