The Tigers suffered a bout of stage-fright in a below-par first 45 minutes which was indicative of their recent inconsistent form, and it was, therefore, no surprise when they fell behind to a sumptuous 20-yard effort from Troy Deeney on the stroke of half-time.
Hornets stopper Jonathan Bond pulled off three smart stops in quick succession after the interval while Hull goalkeeper David Stockdale made a fine intervention himself to deny Deeney a second.
And while neither team came close to replicating the type of performance which has lifted them to the table's upper reaches, it was the visitors who claimed the spoils ahead of their weekend meeting with leaders Cardiff.
The visitors slowly grew into the game with Cristian Battocchio lashing over the crossbar before Czech Republic international Vydra was halted by a fine Abdoulaye Faye block.
At the other end, Robbie Brady cut inside before drilling over and Jack Hobbs' header produced a comfortable save from Bond.
Yet it was Watford whose slick passing was proving more effective and they were good value for the lead Deeney gave them four minutes before the interval.
Almen Abdi and Vydra were both involved in the build-up and Deeney produced a glorious right-footed curling finish from the edge of the area which Stockdale could not prevent flying into the top corner.
However, the hosts could, and probably should, have been level prior to half-time when an unmarked George Boyd fired straight at Bond's feet from eight yards out.
The KC Stadium faithful were soon on their feet after the break when they thought Bond had turned Jay Simpson's rifled effort in, yet the ball dropped just the wrong side of the post.
As the home side pushed forward, though, Vydra uncharacteristically shanked over before Stockdale stayed tall to block Deeney at his near post with Watford serving notice of their counter-attacking threat.
Tigers boss Steve Bruce then turned to big-money signing Nick Proschwitz in an attacking substitution as injured centre-back Hobbs made way.
Yet Hull did little to trouble Bond, Simpson drawing him into a routine save with a header while Proschwitz was unable to control when free in the area, as Zola's men ended a three-game winless streak to tighten things up in the race for the Premier League.