The former UFC heavyweight interim champion survived an onslaught by his Australian counterpart to win via KO in the third round.
Gane controlled distance and picked his shot in the opening round, earning a point advantage. But Tuivasa came out strong in the second, sitting Ganne down with a powerful right hand.
The heavyweight slugged it out in the third, with both fighters nearly ending the fight. But after a series of body blows, Tuivasa tired, and Gane took advantage of his exposed head for a violent finish, delighting an incredible French crowd.
Gane fought division champion Francis Ngannou for the belt in January this year, but lost via unanimous decision.
With Ngannou still recovering from knee surgery, Jon Jones still yet to come back and Stipe Miocic seemingly out of favour, it's anyone's guess what's next for Gane, who is just focused on the belt.
"I think nobody is knowing what's going to happen," he said about his next fight.
"They had a big turnover in this division at this moment. I don't know if there's going to be an interim title.
"I don't know when he is going to come back if he stays in the division, Francis. I don't know when he wants to fight (or is) able to fight. I don't know exactly, but no matter who. I say every time, anyone-anywhere. But now I'm looking for the belt, yeah."
In the other co-main event, Whittaker took middleweight challenger Marvin Vettori apart over three rounds for a dominant win.
Speed became an issue for the Italian as the fight continued, with Whittaker darting in and out, landing shots while Vettori struggled with his range. While he showed an impressive chin, the judges all ruled in favour of Whittaker.
While the Australian acknowledged that the indomitable Isreal Adesanya holds the middleweight belt, he claimed he's the most dangerous man in the division.
"I'm hunting that gold still... so I'm always going to lurking around, just destroying who they put in front of me until I get a chance to gobble up that gold," he said.
"I'm the most dangerous man in the division. Israel's the champ. He beat me twice. Hat's off to him for that. He's a great fighter, he really is. And I think stylistically he's a great fighter.
"I still think I'm the most dangerous man in the division because I win. I win a lot, and I make people hate fighting and I take the fight out of them. That's what I do. I get in there and I get to work."