Deeney exchanged passes with Vydra on nine minutes, but his close-range effort was well saved by David Forde.
Moments later it was the Lions who had the lead when Martyn Woolford slotted home after good play from Scott McDonald.
Juan Paredes's effort almost restored parity for the home side, but Forde was again equal to the effort shortly after the goal.
Watford equalised with nine minutes of the first half remaining when Vydra's deft clip ended up in the net, before Tozser hammered in a free kick in added time.
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The Lions were presented with an early chance to level after the restart but Byron Webster headed wide at the back post four minutes into the second half.
The home side began to find their rhythm and some neat interplay between Munari and Vydra almost released Deeney, but Forde was alert to race off his line and clear.
However, the Hornets weren't to be denied and Munari extended the advantage with his second Watford goal just after the hour mark.
Magaye Geuye was denied a goal by Daniel Pudil on 73 minutes when the Watford man cleared off the line.