Both guys are tired but this kind of fight favors Cain over JDS. Junior has always relied on using his energy sparingly and being able to engage and distance himself from his opponent with his footwork. He doesn't have a high workrate like Cain does, he mostly counters and rests.
Cain on the other hand is a grinder, if he gets tired his fighting style works to his favor. He's capable of pressing forward because he doesn't need to jump in and out of his opponent's range, he just needs to keep pressing forward. While I would said Cain has the better cardio, this is also a styles clash where JDS's gameplan and style are affected much more than Cain's.