It was a performance that gave their youthful and exuberant manager, Adrian Boothroyd, cause for ample satisfaction, but he was at pains to prevent anyone, most of all his players, from getting carried away.
"We are not even halfway through the season," he said, before adding with the suggestion of a grin: "Third will do for now. I'm pleased. But if I get too excited I'll get a slap in the face. From myself. Or from my wife. We need to make sure we keep building and really give the people here something to cheer. We are in this for the long haul."
If Watford can keep hold of such willowy talents as Anthony McNamee, who proved a persistent torment on the left flank, and Ashley Young, who claimed his ninth goal of the season, they can match the exploits of previous teams of their parish in reaching the top flight.
For now, however, Watford can reflect upon a result that became all the sweeter in the knowledge that they were hopping over their local rivals Luton following their hammering at Sheffield United. The Vicarage Road cup brimmeth over...
Danny Shittu's headed goal in the second minute of added time provided a justified scrap of consolation for Rangers' efforts. But Ian Holloway, industry personified as a player, was not satisfied.
"After the second goal our heads dropped, and I'm not having it," he said. "We've got a weak underbelly."
But Watford had too much flair to contain, even though it took them 39 minutes to get their eager noses in front as McNamee's teasing dink of a cross from the left offered Young a clear far-post header and, although his effort was blocked, Matthew Spring lived up to his name to guide the rebound home.
Watford went into a 2-0 lead through McNamee's cross shot with 20 minutes remaining, and their happiness was made almost complete when Young added a further goal with a cross-cum-shot from the left six minutes later.
Watford (4-4-2): Foster; Doyley, DeMerit, Carlisle, Chambers; Devlin, Spring (Al Bangura, 88), Mahon, McNamee; King, Young. Substitutes not used: Chamberlain (gk), Stewart, Mackay, Henderson.
Queen's Park Rangers (4-4-2): Royce; Bignot, Evatt, Shittu, Dyer; Ainsworth (Cook, h-t), Docherty, Santos (Nygaard, h-t), Gallen; Moore (Langley, 74), Sturridge. Substitutes not used: Cole (gk), Milanese.
Referee: M Atkinson (West Yorkshire).