While the victory was the Hornets fourth in succession at Vicarage Road, all the headlines will deservedly go to Lloyd Doyley.
The left-back had never scored in his previous 268 outings for his only professional club but he finally addressed that record in some style shortly before the break.
It looked like Patrick Agyemang's 34th minute opener against the run of play would be enough to give the visitors the lead at the break.
The striker arrowed a shot into the bottom right-hand corner after being picked out by Alejandro Faurlin, but then came Doyley's special moment.
Jon Harley started the build-up with a deep cross from the left which Don Cowie met on the half-volley with a ball back across the six-yard area and then the unmarked Doyley flung himself full-length to head past Radek Cerny.
It was no more than the home side deserved against a team who extended their number of games without a clean sheet to nine and after the restart Malky Mackay's men took charge.
Watford could have been infront within 20 seconds of the restart as Cerny superbly tipped Nathan Ellington's header onto his near post.
But their second did arrive in the 56th minute. Danny Graham's deft header inside allowed Tom Cleverley to break at pace at a square Rangers defence and as he approached the edge of the penalty area, the Manchester United loanee slipped the ball to his right for Cowie to crack a fine low drive across Cerny to net his first of the campaign.
Rangers huffed and puffed in search of an equaliser without really threatening and they were undone for a third time on the counter-attack deep into injury time when Graham's ball from the right put Cleverley through one-on-one with Cerny and the midfielder kept his composure to score his seventh of the season.