Fū happens to be a sensor and Torune is one of the worst shinobi to fight in close quarters.
Basically, the former notifies Torune when Zabuza is approaching and he touches him.
Also, Fū should be able to accurately use the Mind Body Switch Technique in the mist. (he can shout out where he is)
The Mind Puppet Switch Cursed Seal Technique would also end the match. (he either had it on him or made it on the run)