LOS ANGELES — Chael Sonnen has never fought as a heavyweight at any point in his long careers in wrestling and mixed martial arts. He'll make his debut in the marquee weight class this weekend at Bellator 192 against Rampage Jackson, who outweighed Sonnen by a whopping 31 pounds on the scales Friday.

Sounds crazy, right? Even Sonnen knows it.

"I don't totally know what I'm getting into, in fairness," Sonnen said. "I've had workout partners that were heavyweights, but I don't know what that power will feel like. I imagine I'll move out of the way."

Sonnen just couldn't resist the chance to chase the Bellator title belt in an eight-man tournament starting Saturday night at the Forum. The Heavyweight World Grand Prix will be the centre of Bellator's promotional efforts in 2018, showcasing a host of well-known MMA stars including Fedor Emelianenko, Frank Mir and Roy Nelson.

Bellator was founded a decade ago around the tournament concept, but strayed away from it in recent years to maximize its ability to stage big fights.

The promotion's return to something resembling its roots begins in Inglewood with the 40-year-old Sonnen against the 39-year-old Jackson, who tipped the scales at 253 pounds. To Sonnen, the excitement of the undertaking outweighed the obvious drawbacks in competition.

"It's the only fair way to do things," Sonnen said of the tournament format. "It's just that in combat, we don't have to do things fair. We can do things that are good for entertainment and good for business. In this case, (Bellator President) Scott Coker is risking everything. He doesn't know what the biggest fights are going to be. He doesn't know how it's going to play out, but he said, 'I'll do it fair for a change.' And here we are."

While the UFC waits for new stars to emerge — or for its biggest existing star to get tired of spending his boxing money in Ireland — Bellator is building its year around the tournament designed to crown its first heavyweight champion since 2016.

The promotion is doing it with its usual mix of sports and spectacle, pitting veteran heavyweights against smaller, bulked-up stars closer to their prime, including Ryan Bader and Muhammed "King Mo" Lawal.

It could be fascinating competition, or it could produce physical mismatches and lopsided decisions. Either way, Coker expects it to be compelling.

"It just snowballed into something we needed to do," Coker said. "We already had good heavyweights, and pretty soon we had eight marquee names. This was the thing that made the most sense, and it's going to be an all-yearlong story line."

Jackson is no stranger to weight-cutting struggles — he only recently realized ketchup has sugar in it, he said — but the veteran fighter has no such worries now. He hadn't even weighed himself in two weeks before his bout, and he munched on chicken skewers before his fight-week news conference.

Jackson and Sonnen get along well, but Sonnen still managed to get in an early jab at his thicker opponent: "I agreed to fight at heavyweight, not superheavyweight!"

For Coker, there were actual hurt feelings to smooth as well.

Sonnen and Jackson are being showcased in the main event after former UFC star Rory MacDonald takes on welterweight champion Douglas Lima for the title. MacDonald had thought he was in the main event until last week.

"I was disappointed when I heard about it," MacDonald said. "I was bummed out. I was a little bit hurt. It didn't affect my sponsorships, but I felt upset. I just put it out of my mind. These are the moves they have to make. I have a job to do, and their job is to make their business successful."

Bellator 192 is the first event since promotion owner Viacom officially rebranded the Spike network as the Paramount Network on Thursday. While MacDonald and Lima are among the world's best handful of fighters at 170 pounds, Jackson and Sonnen are stars with far more name recognition, and executives from Viacom understand what draws viewers to this promotion.

When asked if he was concerned about the rest of his roster's reaction to Bellator's decision to showcase heavyweights in all of their tournament bouts, Coker laughed.

"I don't think they'll have any problem cashing those checks on Monday," he said.