Jose Holebas scored the only goal of a largely uneventful game as Watford returned to winning ways and Boro saw their wait for a victory extend to six matches.
Boro went into the match having recorded one of their worst starts to a Premier League season ever, and there weren't many signs of it improving throughout this afternoon's contest as both sides struggled to create clear goalscoring chances.
The biggest talking point of the opening 45 minutes surrounded referee Roger East, who opted not to show Antonio Barragan a second yellow card for a cynical challenge when he may well have been sent off.
If Watford felt aggrieved at the referee's inconsistency then much of the ill feeling will have dissipated when they took the lead less than 10 minutes into the second half.
The goal came in some style too, with Holebas advancing to the edge of the area before lashing a stunning strike past a helpless Victor Valdes and into the top corner.
The memorable strike continued Watford's impressive run of goalscoring against Boro having now found the back of the net in 16 of their last 17 meetings, but Walter Mazzarri will still have been concerned at the other end of the pitch due to the Hornets not having kept a clean sheet in 12 games.
Middlesbrough, who are yet to pick up a home win this season, only sit outside the relegation zone on goal difference, while Watford climb up to ninth in the table.