Bellator 206’s main event will be a curious bit of a role reversal for Gegard Mousasi.

The Bellator middleweight champion has made a career out of often playing the David to his opponent’s Goliath. Over his 15-year run in the fight game, Mousasi spent large swathes of his time competing as an undersized fighter in both the heavyweight and light heavyweight divisions to great success, capturing the Strikeforce 205-pound title and even submitting current UFC heavyweight Mark Hunt with a 79-second armbar in Japan.

But this Saturday, for the first time in a long while, Mousasi will see the tables turned when he meets Bellator welterweight king Rory MacDonald in a much-anticipated champion vs. champion superfight at Bellator 206. For once it is Mousasi who will be the bigger man on fight night, and the 33-year-old had to rack his brain to remember all the way back a decade to recall the last time he truly enjoyed a meaningful size advantage over an opponent.

“This will be the first time I believe I have a size advantage since [2007],” Mousasi told MMA Fighting, laughing. “I fought a long time ago in Canada, I fought a Croatian guy, I don’t remember his name, but there I had a size advantage. At the end, I explained to him about cutting weight. He didn’t know about weight-cutting, so I explained to him, and I was bigger than him at that time. But I think this is the first time I get an actual advantage.”

Mousasi is likely thinking of Damir Mirenic, a Croatian journeyman who he defeated via first-round TKO back in the autumn of 2007. But for whatever talents Mirenic may have had, there’s no doubt that MacDonald presents a far more significant challenge.

The reigning Bellator welterweight champion, MacDonald can legitimately be called one of the best 170-pound fighters in the world today. He owns a dominant 2014 win over current UFC welterweight titleholder Tyron Woodley and is a perfect 2-0 under the Bellator umbrella, having stopped Paul Daley with a second-round submission in his promotional debut then captured the 170-pound title with a gutsy win over Douglas Lima in his sophomore outing. In fact, it is MacDonald who sought Mousasi out from the start.

Similar to the way his mentor Georges St-Pierre hunted down the UFC middleweight title, MacDonald called for the champion vs. champion clash against Mousasi soon after besting Lima, so Mousasi doesn’t want to hear any criticism about picking on the smaller man.

“Rory, he started it,” Mousasi said. “He wanted to fight. Obviously we felt like it was a good matchup, a good fight for me, and we said we would like to face him. Going back and now watching fights of Rory’s, I was thinking, ‘Wow, I chose the toughest guy,’ so maybe not the smartest choice. But it’s definitely going to be a good fight, I believe. He’s a big challenge for me, I believe.

“We saw ‘GSP’ versus Michael Bisping, and ‘GSP’ won. We saw Daniel Cormier, he went up, he won. That 10 pounds that I have over Rory is not going to decide if I’m going to win or not. I went to light heavyweight and heavyweight, I was successful there also, so [size] is not going to decide if I’m going to win. I didn’t hesitate to take the fight, but you know people are always — if I beat him easily, people are going to say, ‘You beat a welterweight.’ And that’s not the case. Kelvin Gastelum is a welterweight; he’s fighting at middleweight, he’s doing pretty good, he’s fighting for the belt. So it doesn’t mean anything.”

Mousasi, like MacDonald, has a 2-0 record in Bellator that took some guts to pull off. In his promotional debut, he stormed back from an early disaster to capture a hard-fought decision over former champion Alexander Shlemenko. He then effortlessly seized the Bellator middleweight throne with a first-round romp over Rafael Carvalho. But while MacDonald may be a smaller man than either of those two, Mousasi isn’t heading into Saturday night expecting anything less than the toughest fight of his Bellator run.

“He’s very well-rounded,” Mousasi said of MacDonald. “He’s a lot better, I think, when you face him in the cage. He doesn’t have anything spectacular like spinning back kicks, the crazy stuff like Anderson Silva. But everywhere he’s really solid, on the ground, his jiu-jitsu, wrestling, stand-up. And mentally, he’s tough. He’s physically there. He has the technique and he’s physically, mentally, and technically solid, so he’s solid and he comes to fight. That’s one thing I’ve seen against Robbie Lawler, he comes to fight, he has the mentality, so that makes for a very dangerous opponent. He’s a complete fighter.

“I’m just planning to be the better mixed martial artist. I’m planning to outsmart him. I feel like I have the better stand-up, so I’m going to try to take advantage of that. If I feel like I’m losing in the stand-up, I will try to out-power him. If that doesn’t work, I’m going to try to make a fight out of it. There’s a lot of options that I can take to win the fight, but if I feel like I’m not getting the job done, then I’ll make a fight out of it. Maybe overpower him. There’s a lot of things, but the first plan is the be the better fighter.”

If things go well for Mousasi, he hopes to use Bellator 206 as a springboard into a busy 2019 campaign that could signal the end of his time at 185 pounds — or potentially his career.

Although he is only 33 years old and still in his fighting prime, Mousasi admitted he is beginning to feel the mileage on his body’s odometer starting to mount. He said there’s a chance his current Bellator contract may be the last of his career, and with Bellator’s middleweight division finally restocked with potential contenders like Rafael Lovato Jr. and Lyoto Machida, Mousasi is eyeing one final good run to cement his time at 185 pounds.

“I have to beat Rory first, but if I beat him, I want to get right back in, so I want to get it done as quickly as possible, hopefully with a good result and then look forward to the next fight, next challenge,” Mousasi said.

“Machida is fighting in December. So if I win, I would fight [Lovato Jr.] in January, and then I’ll fight Machida in Holland in maybe April or something like that. That would be the best scenario, but I’m just thinking. I’m not overlooking Rory MacDonald.

“I want to get fights done. Three more fights at middleweight [after Bellator 206], and then my contract is up,” Mousasi continued. “After that, it depends — I retire or I go a division higher, and I will be done with middleweight. I won’t be coming down anymore.”

Mousasi said his decision regarding retirement will largely depend on how his next four fights go, beginning with MacDonald. But if things go well and he feels he is still able to compete, he could see himself returning back to his old-school roots and closing out his time in the sport with a one more David vs. Goliath jaunt through the light heavyweight and heavyweight divisions.

“I think as I get older, I’m going to look for the fun fights. Maybe heavyweight, light heavyweight. I’m tired of the weight cut, so I’ll want to fight at the highest levels for these four fights, and then from there fight old men,” Mousasi said, laughing. “I don’t know. I think I will be close to the end of my career, so if I continue to fight, I would like to have more comfort. I don’t want to lose a lot of weight anymore. I’ll fight heavyweight too, I don’t have a problem with that.

“I always said after these four fights, I would want to retire, but like I said, everything depends on the result. If I win every fight in four or five minutes, I keep winning, yeah, the desire will be to continue. But if I have fights like Shlemenko, then I have to rethink [things].”