The Hornets made two changes with a nod towards the FA Cup final as Christian Kabasele and Etienne Capoue returned, while Manuel Lanzini was one of those to return for the Hammers.
In gorgeous sunshine in Hertfordshire, the home side started well, having a Gerard Deulofeu goal chalked off for offside in the first minute.
However, it was the Hammers who took the lead, with Noble the hero on 15 minutes after a fine strike.
The skipper picked the ball up on the halfway line, played a one-two with Michail Antonio, dropped a shoulder to take Kabasele out the game and slotted home past Ben Foster.
That seemed to spark Watford back into life but they were met with stern resistance and on 39 minutes, the Hammers went 2-0 up when Lanzini followed up Antonio's shot that came back off the bar, courtesy of a fine save from the unlucky Foster.
The second half started with a bang when Deulofeu finally got his goal, latching onto a poor back pass by Pablo Zabaleta and the Spaniard took advantage to skip by Lukasz Fabianski and into the net.
Watford shot themselves in the foot soon after though, when Jose Holebas found himself out of position and brought down Antonio, receiving a red card that rules him out of next week's FA Cup final.
The hosts initially responded but could not get back on level terms and it was game over on 71 minutes when Marko Arnautovic followed up Felipe Anderson’s volleyed effort which again Foster had saved onto the post.
Noble completed the rout from the spot with 12 minutes left to see the Hammers finish in the top half, while for Watford, they have work to do ahead of next week’s trip to Wembley.