Since the air inside the balloon is slightly greater in pressure than the pressure of the air on the outside (the difference is related to the strength of the elastic rubber material) the reaction is an EXPLOSION... an implosion would occur if the pressure inside was LESS than the pressure outside. But for that to happen the container would have to be strong enough to withstand the pressure differential.

It's really more of a burst than either an implosion or an explosion. The air inside of the balloon rushes out of the hole, and the air outside of the balloon squeezes the balloon in shape back to its unexpanded form, which of course squeezes the air inside even more strongly. It might be easier to imagine what it looks like if you have a water balloon instead of an air balloon, but it's basically the same process.