The Gunners scored the only goal of the game on 10 minutes through Pierre-Emerick Aubameyang who blocked Ben Foster’s attempted clearance.
Just a minute later Watford were reduced to 10 men when captain Troy Deeney was shown a straight red card for an elbow on Lucas Torreira.
The Hornets, however, are no mugs and Javi Gracia’s men could consider themselves unfortunate not to take anything from the game after carving out a number of decent openings and keeping the Gunners on the backfoot.
The closest they came, however, was when Adam Massina rattled the angle of crossbar and post from fully 25 yards with an arrow of a strike that certainly deserved better.
Arsenal, however, were not without chances of their own with Henrikh Mkhitaryan and Aubameyang spurning perhaps the best of these to make the game safe.
As it is, the victory was enough to take Unai Emery’s side back up to fourth and put them in the driving seat to claim a return to the Champions League next season.