How did bilbo escape Gollum? Was it wits or luck?

I would not really call it either. Gollum and Bilbo play the riddle game. Unfortunately for Gollum (he has been in a dark swamp for centuries) he is losing. Bilbo has the ring already. Gollum blocks Bilbo's exit but Bilbo uses the invisibility of the ring to get away. Bilbo had the sense to have the ring in his possession before the game but that is about it.