The Rocket found himself trailing 4-3 to the Belgian at one stage, but three back-to-back sets and late impressive breaks of 143 and 120 helped the Englishman complete the turnaround.
The event was the first World Snooker Tour event held in mainland China since 2019 - before the coronavirus pandemic - as well as the first since a spate of match-fixing scandals hit the sport with a particular focus on its Chinese players.
It was O'Sullvian's fifth Shanghai Masters win overall, adding to his wins in 2009, 2017, 2018 and 2019.
He had beaten the likes of Mark Selby (40) and John Higgins (48) en route to Sunday's final.
Speaking afterwards, O'Sullivan revealed he wasn't at his best and heaped praise on his beaten opponent: "It was one of those tournaments. I was well below par, but I played alright when I had to," he said.
"I'm not surprised Luca has done as well as he has. He's not a surprise world champion.
"He's got an amazing gift to play this game," O'Sullivan added.
The newly crowned champion also confessed he rarely keeps his trophies and that he was likely to gift this one to a friend.
"I'll be giving the trophy to my friend who is opening up a club here. It will be staying in China," he added.
"I always give them away. My mate Paul's got one, I gave one to a kid in the crowd.
"I'm not really bothered about trophies. I've sold quite a few of them.
"I don't want any memorabilia left by the time I'm 70 or 80. I'm preparing for death - part of that is I don't want no snooker stuff - waistcoats, cues, it's all going to go."
