Etienne Capoue's stunning 50th-minute strike set the Hornets on their way to victory at the Lamex Stadium before summer signing Jerome Sinclair came off the bench to wrap up the win in the final minute.
Having fielded a strong side, it proved to be a comfortable evening for Walter Mazzarri's men in Hertfordshire.
elastico superfly orange Odion Ighalo had two efforts cleared off the line in the first half, the first coming when Boro 'keeper Jamie Jones raced back to cut out the Nigerian's chipped effort in the opening stages.
MagistaX Proximo orange After Capoue had lashed a wild effort over the bar, the Frenchman turned provider, laying the ball off for Ighalo, who saw his goal-bound effort cleared by Fraser Franks.
neyjar jordan cleat That kicked Stevenage into gear before the interval as Matt Godden fired narrowly over the target in what proved to be the final chance of the game.
It took Watford just five minutes to break the deadlock after the break as Capoue picked up the ball on the right, cut inside a Stevenage defender and rifled an unstoppable shot into the top corner of Jones' goal.
ACE 16+ PureControl Watford continued to apply the pressure but Abdoulaye Doucoure failed to make their most of the Hornets' dominance as his shot was blocked and Ighalo struck the crossbar with the rebound.
Mercurial Superfly V orange Stevenage's resolve was broken for the second time in the closing stages as Sinclair grabbed his first Watford goal, heading home Almen Abdi's cross to seal a good evening for Mazzarri and his team.
The Hornets have one final pre-season fixture remaining - against QPR on July 30 - before switching their focus to the Premier League opener away to Southampton on August 13.
