Marvin Sordell notched his third goal in two games inside the opening two minutes when he slammed home a loose ball and Danny Graham's deflected strike in the opening exchanges of the second period ensured the Hornets breezed past a lacklustre Bristol City at Ashton Gate.
The winning margin could easily have been more than two goals as City were reliant on David James to keep a look of respectability to the scoreline, with the former England keeper making fine saves to deny Sordell and Will Buckley.
The assured victory moves Watford into the top half and ends a four-game winless streak in the league, a run stretching back to their 3-2 win at Norwich.
The defeat for Keith Millen's men means they are unable to build on Saturday's first win of the season at Scunthorpe and have picked up just one point from their first three games on home soil.
Millen named an unchanged side following Saturday's success, while Sordell's two-goal salvo against Doncaster earned him a start in Watford's line-up.
And it proved an inspired decision by boss Malky Mackay as Sordell put the Hornets ahead inside the opening three minutes.
The 19-year-old had already brought a fine stretching save from James and from the resulting corner, Sordell pounced on Adrian Mariappa's knock down to slam home.
It was a flying start for Mackay's men and they could have doubled the lead moments later, but Danny Graham could not find the target from a good position inside the box.
Watford's dominance continued and Sordell almost added a deserved second on the 20-minute mark, but James proved his quality again with another fine parried save.
Bristol City rarely threatened throughout a disappointing first period, with Brett Pitman's effort from the edge of the area their only real moment of promise.
And the start to the second half followed an identical pattern to that of the first as Watford got on the scoresheet early on again to double their advantage.
John Eustace got on the ball in his own half and pumped a long ball down the field, which Graham latched onto and fired home with the help of a deflection.
If the home side were to get anything out of the game then they had to up the ante and they tested Watford keeper Scott Loach for the first time soon after.
Half-time substitute Danny Rose, on loan from Tottenham, picked up a loose ball on the edge of the area and fired in a low shot, which Loach did brilliantly to keep out.
But Watford were soon back on the front foot and James was the saviour for his side again as he did well to keep out Buckley's effort from distance.
It was a poor performance from Millen's men and they were unable to find a way back into the game as Watford held on for the points.