Knife to the brain could possibly KO/incapacitate Victor enough to count as a win (knife to the brain certainly made Deadpool loopy for a bit). But the chances of Riddick being able to sneak up on him to do it is slim, considering Creed's heightened senses. And in a pure straight up fight Creed would win IMO. He'd just heal from any knife wounds, where as every claw strike that connects is going to be another nail in Riddick's coffin.
deadpools healing ability took a few seconds to heal a knife in the brain after removing it, having that knife in his head would have killed him until it was removed but he had a awesome regen ability to keep him alive with it in his skull.
victor doesn't have a regen that advanced but is still enough to keep him coming back. that's why I am with victor, he is faster (not by too much) has heightened senses and is a more brutal killer