I think that GSP will survive an early scare and assert his authority for the first two rounds. The third round will be a back and forth but in the third minute GSP will rock Hughes with a powerful shot, Hughes will go down and GSP will go on him. Hughes will be stunned but will still get half guard... the crowd will hold its breath, when, suddenly...
Ross Pointon will descend into the Octagon by parachute, and will land on St. Pierre, driving St. Pierre down onto Hughes and knocking out both of them.
The judges will consult the NASC handbook, and will discover and old, unchanged law that says that if a 3rd party knocks out both contentders in a title fight by means of parachute entry, he is crowned winner of the fight and the title.
And Ross Pointon will be crowned welterweight champion of the world. Or at least the UFC.