It doesn't play out the way you probably think it does.
It bears mentioning that this is not a no-holds-barred engagement. In modern fencing, a large portion of the body – sometimes the entire body – is a valid target; but in this exercise, the aim of expert and amateur alike is to puncture a balloon on their opponent's chest. This, one would think, puts the master fencers, with their superior dexterity, at a distinct advantage. And yet, the three of them are seriously outnumbered. So what happens? Do the professional fencers dominate, or are they overwhelmed?
Well... neither, actually. Jason Kottke gives a good summary of the dynamic that takes shape:
The crowd, being a crowd, does not initially do what it should, which is rush the experts and take them out right away with little regard for individual survival. But pretty much every person fights for themselves. And instead of getting easier for the Musketeers near the end, it gets more difficult. The few remaining crowd members start working together more effectively.
As for the outcome, you'll need to watch for yourself. Suffice it to say, in situations like these, simple hypotheses like "safety in numbers" can fail to account for the uniquely human element in crowd psychology. The human herd is an incredible, if sometimes counterintuitive, thing.