While Pramac Racing team-mate Jorge Martin had qualified on pole position and led all the way until midway through the 27th and final lap, Zarco paced himself to perfection and made the decisive move at Miller Corner.
In doing so, the 33-year-old Frenchman finally became a MotoGP grand prix winner, in his 120th start, and after 19 prior podiums.
He said post-race that he tried to maintain the belief that a victory would come one day, but that it was stretched when his best opportunities always seemed to pass him by – until now, when the situation suited his strengths.
“I tried to keep this hope always there,” said Zarco.
“But, it seems that the fight now, even if you get to the podium, it's a fantastic thing anyway.
“But, in the moment I could win races, it was another rider that was flying this day, and then you are wondering what's up and why I don't have this moment like the others can have.
“But today, I got a little bit more of this moment, not going in front of the race and going away, but almost in my strategy to have this control of the rear tyre and finally get the advantage at the end with my style.
“That is good. It was good in the past, but now everything is getting more constant that it's tough now to make the difference.”
Zarco's triumph meant that the trademark backflip which had not been seen since the 2016 Valencia Grand Prix, the final event of his second Moto2 championship-winning season, was back.
He pulled that off in front of the Phillip Island crowd on the cool down lap but, apart from that, was relatively calm in light of what he had just achieved.
“A journalist asked me if it was like an explosion in the helmet, if I screamed or not,” recalled Zarco.
“No, I feel almost like everything so calm in that moment.
“It was like, ‘Okay, this is it, it's done, and it's so good,' and then the emotion came up a bit.
“I was also very happy to get the congratulations from, not all the riders, but many riders opened the helmet and I could see the eyes, they were happy for me, and this brought me a very nice emotion.”
Despite the Japanese marque's struggles in recent years, he believes further victories are not out of the question, even if the Desmosedici is currently the bike to have.
“Sometimes, I was thinking that the light is still there, the hope is still there, even for the future with Honda,” remarked Zarco.
“Because, as long as you're a competitor in different conditions, maybe there will be opportunities even if the bike is not, at the moment, so competitive as the Ducati.
“But it was necessary with the Ducati, in normal conditions, to have this victory.”
The result was in fact another all-Desmosedici top three, although Martin faded to fifth after he opted for a soft Michelin rear tyre when most went for the medium.