Go watch the Kos and Story fights. Both wrestlers controlled him and nullified his striking. In both fights he tired visibly by round three. If they can do it GSP will do it. I've seen nothing from Hendricks that makes me think he has more than a punchers chance.
Yeah, it's MMA math, but if Kos was able to out wrestle Hendricks (and he did, stopping all of Hendrick's attempts and taking him down for some G&P in the 3rd,) then GSP will have a field day .. that and a 7" reach advantage (Hendricks will have to stop for lunch on the way to GSPs jaw whenever he swings his left hook,) and GSP's tons more speed on the jabs and superman punch, 5 rounds, and Hendricks will need to get really lucky with his only real weapon, his lunging hook.