the way i see it going down goes like this-
spider-man has the major speed advantage and the symbiote makes him a total bastard so he will be dodging and punching all over the place, and talking smack too.
after like a minute, spider-man will be feeling that he is winning but just as he starts another punch flurry, spawn just turns into a pin cushion severely damaging spider-man's hands (IMO the spider-sense can't know that would happen).
spawn then uses the time to do any array of attacks to end it; chain choke, spiky chain garrote decapitation, impaling spider-man, blasting him with eldrich energy, putting his spiked fist through his head, etc.
spawn for the win.