In my opinion, the only way Kovalev wins this fight cleanly is if he catches Hopkins with a good shot before he really realizes he's in danger, and knocks him out.
Otherwise, the more likely scenario is one of the following:
a. Koralev gradually establishes that he's just too young, strong, and fast. This causes Hopkins to go into panic mode. The pace is too fast for him to sneak in a dirty headbutt, so he instead dreams up some weird illness or fakes a low blow (Super Joe, déja vu) or just runs out of the ring or stops fighting and says he got hit with a mysterious illegal blow. The fight ends in controversy, and Hopkins of course will say a lot of racist things and not give Koralev ANY credit. Hopkins will find a way to claim victory.
b. Hopkins wins on cuts, thanks to illegal headbutting.
Whether A or B, Hopkins will CHEAT.
That's his only chance, unless he catches Koralev with his amazing knockout power (L, O, effing L).
Hopkins is a cheater and a phony, and was exposed by Calzaghe.
Koralev needs to either knock him the F out, or be prepared for some weird, professional wrestling style dramatic ending.