Re: No defence?
First of all: I hope the guy is okay, and that you are too. It must have been a quite unpleasant experience.
Defence aganist that attack would probably not be possible once the situation has gone so far as you describe. Maybe there is the odd chance that a very skilled martial artist would have reacted on the shift of the guys balance, flicker in the eyes or what ever other sign one can pick up.
In my opinion the best defence in this particular situation is to not get into such close contact with a possible assailant - nor to allow the situation to escalate to such a point. This is a lot easier said than done, but the sooner a dangerous situation can be sensed, the easier it can be avoided.
If somebody really want to hurt you, and they are cold and experienced enough to lure you into a situation to there advantage, then there is little to no chance of getting out of it unharmed regardless of how much practice you have. A knife, a gun, a hand grenade... something will be more than you can cope with.
Once again - I hope the victim is okay.