I've had a theory since I watched the Gatti vs. Ward trilogy (one of the greatest in boxing history), that the third fight generally favors the winner of the second fight in a 1-1 trilogy. I compiled a list of well known trilogies in MMA and Boxing to see if there's enough data for statistical evidence
MMA:
GSP vs. Hughes: Hughes, GSP, GSP
Cruz vs. Faber: Faber, Cruz, Cruz
Cain vs. JDS: JDS, Cain, Cain
Chuck vs. Randy: Randy, Chuck, Chuck
Penn vs. Hughes: Penn, Hughes, Penn
Forrest vs. Ortiz: Ortiz, Forrest, Forrest
Melendez vs. Thomson: Thomson, Melendez, Melendez
Stout vs. Fisher: Stout, Fisher, Stout
Bas vs. Frank: Frank, Bas, Bas
Sylvia vs. Arlovski: Arlovski, Sylvia, Sylvia
Total third fight record: Second fight winner 8 - First fight winner - 2
I'm sure I missed some 1-1 trilogies here, so let me know.
Boxing:
Gatti-Ward: Ward, Gatti, Gatti
Michael Carbajal-Humberto Gonzalez: Carbajal, Gonzalez, Gonzalez
Ali vs. Norton: Norton, Ali, Ali
Patterson vs. Johansson: Johansson, Patterson, Patterson
Griffith vs. Benny Paret - Griffith, Paret, Griffith (Paret died in the ring unfortunately)
Barney Ross vs. Jimmy McLarnin - Ross, Mclarnin, Ross
Barerra vs. Morales - Morales, Barerra, Barerra
Zale vs. Graziano - Zale, Graziano, Zale
Ali vs. Frazier - Frazier, Ali, Ali
Leonard vs. Duran - Duran, Leonard, Leonard
Duran vs. De Jesus - De Jesus, Duran, Duran
McLarnin vs. Ross - Ross, McLarnin, Ross
Pacquiao vs. Morales - Morales, Pac, Pac
Vasquez vs. Marquez - Marquez, Vasquez, Vasquez
Total third fight record: Second fight winner 10 - First fight winner - 4
Total: 18-6 75% wins for the winner of the second fight
Why is this the case? There are a few reasons.
1. A "fluke"
Example: JDS KO'd Cain in the first fight, and people were wondering if it was a fluke, so they had a rematch to see. If JDS had won, there would have been no trilogy, and the "fluke" talk would have ended. However, Cain won decisively. After two fights, it seemed kind of clear that Cain was the better fighter and the first fight was a fluke. However, because JDS won the first fight, it was enough to warrant a third fight, which Cain won the same way he won the second fight. Domination and fluke verified.
2. Too young/too old
Example: Cruz vs. Faber. Cruz was very green when he fought Faber the first time. He hadn't really come into his own and developed the style that would carry him to being one of the best 135ers of all time. By the time they had their rematch 4 years later, Faber was already on the decline (though still extremely formidable). The third match was another 5 years later, and by then Cruz had been through several injuries, but still proved to be fresh and strong, and Faber had clearly declined by then.
3. Making the adjustment
Example: Chuck vs. Randy. In their first fight, Chuck underestimated Randy (especially his power in the clinch) in their first fight, and was gassed in grappling exchanges, eventually leading to being taken down, mounted, and TKO'd. In the rematch, there was controversy with the eye poke prior to the TKO, but it was clear that Chuck had made adjustments with keeping range and counter striking against Randy's aggression, which is what won him the third fight.
Do these things apply to Stipe vs. DC 3?
1. A "fluke" - The first fight's KO certainly had the feel of a fluke. Though the second fight didn't really do much to confirm the "fluke", as DC was holding his own in the second fight until the end. Still, there is still somewhat of a fluke feeling around the first fight, especially after Stipe's quick turnaround from fighting Francis Ngannou, and people speculating that his chin hadn't had ample time to recover. (I don't really understand the biology of all that, but whatever).
2. Too young/too old - Stipe certainly wasn't too young or green in their first fight. He had already established himself as a Heavyweight GOAT candidate. However, DC is fighting his final fight, and he is quite old with a lot of mileage on him. He took a LOT of damage in the second fight both to the head and the body. Though Stipe also got beat up pretty badly. I still see DC as fading in his career, and DC's age could be a major factor.
3. Making the adjustment - Interestingly, we saw the adjustment factor in during the fight. Stipe found DC's body which led to a fast and sharp decline in DC. That adjustment played a major role in Stipe's win. If DC has no answer for Stipe's body shots, it will be an ugly fight for DC.
I'm shocked that so many experts are picking DC to win the third fight. It could certainly happen, but all signs, in my mind, point to Stipe winning the trilogy.