You're a comic book writer working on a major crossover event, with the outcomes predetermined by your editor or fan vote. You have no control who wins, but you have complete creative control over the details of the fight.
Your job is to make the fights as plausible as possible, while being as respectful as possible to both characters.
And complete creative control means just that: You can use plot devices if you need them, or play somewhat fast and loose with what a win or loss is, if necessary.. (It doesn't have to be strictly a KO/Battlefield removal deal.)
thor hits supes with his hammer, shattering it to pieces. supes feels bad and puts it back together so quick that thor survives. Supes than flys away, thor wins via bfr