Odin and Highfather want to see wich one is stronger so they put the two in a diffrent dimension with no machines or sentiant life but does have oxegen and a towel 4 lightyears away.
Thor has mjiolnir and no odin force but all other non-odin force feats still count.
Orion has astro harness and can use his mother box only once to regenrate fatal wounds.
Both start fifty feat away Orion is frenzied becuse he has resently found that darkseid was his father after saying "Orion I am your father." and Thor is slightly upset becuse he was in a middle of a date with Jane Foster.
So no prep time for either obviusly and both have no freaking clue who the other is but they both have a bad idea about each other so they attack each other simutainusly.