GSP had no problem with BJ's ground game and he is better, for one round, than Diaz on the ground.
Diaz's only chance of winning is a submission and that isn't going to be easy when you are being smothered and overpowered. I suspect George will pepper him with a jab, take him down when he wants to and most certainly if he is ever losing in the stand up. Nick is overrated. His record was padded in Strikeforce with 2nd rate fighters and beating BJ now at WW doesn't mean so much. BJ hasn't beat anyone in 3 years except a well past his date Hughes. This will not be a close fight. GSP will be beaten when he gets tagged by a hard shot, he has a mediocre chin and that is his weakness. It will take a very slick submission to get him and I don't think Nick has the absolute top notch JJ it will take. He'd have to rock him on the feet with a bunch of shots and GSP get sloppy after the take down.