The full-back's team-mates joke he has never even scored in training, but he cancelled out Patrick Agyemang's opener for Rangers like an accomplished striker with a flying header before the break.
And Doyley, who turned 27 last week, was celebrating further when he had a hand in a goal for Don Cowie before Tom Cleverley wrapped up the win in stoppage time.
Victory was especially sweet for Watford in a clash between the division's haves and have nots - the Hornets are now two points above their rivals even though the gulf between them off the pitch remains huge.
QPR are still bankrolled by their billionaire owners while Watford, by contrast, are facing the threat of administration - and the 10-point penalty which goes with it - unless they can urgently raise funds.
Chairman Jimmy Russo, who has had to lend the club £1million to see them through the month, denied before the game that he needs to sell players in January.
But England Under-21 goalkeeper Scott Loach is thought to be on Tottenham's radar while big earner Nathan Ellington is also likely to move on.
Loach was a virtual spectator for the first half an hour as the Hornets took charge and Ellington teed up Cleverley to fire narrowly over.
Cleverley then headed a Lee Hodson cross straight into the arms of Rangers keeper Radek Cerny.
But in the 34th minute, against the run of play, Rangers took the lead when Alejandro Faurlin's clever pass played in Agyemang, who
rifled a low shot past Loach from the edge of the area.
Rangers were desperate for a pick-me-up after Saturday's 5-1 pasting by Middlesbrough, but their lead lasted just 10 minutes.
Doyley leapt through the air to get on the end of Cowie's cross and bullet a header past Cerny to spark wild celebrations around the ground.
Ellington almost put Watford ahead 20 seconds after the restart but his header was deflected onto the post.
But they did not have to wait long to take the lead when Doyley, on yet another overlap, ignored the crowd's pleas to shoot and fed Cleverley, who in turn picked out Cowie to lash in his first goal of the season.
Cerny saved well from Jon Harley to keep Rangers in with a shout, but as they poured forward in injury time Cleverley was able to breakaway at the other end and slot home the third.