The 32-year old scored one and created another to give the Hertfordshire side a comfortable afternoon at Vicarage Road.
The first chance of the game fell to the visitors after just three minutes, when Sean Maguire picked up a ball from Daniel Johnson to unleash a fierce shot which forced Watford goalkeeper Ben Foster to fingertip over the crossbar.
Indeed, the visitors had by far the better of the opening exchanges, and on seven minutes Brad Potts just curled the ball wide of the left hand post.
Preston almost equalised on 24 minutes through Patrick Bauer from 10 yards out, but Foster was on hand to block his effort.
Watford were forced into a change on the half-hour mark when Andre Gray, making his 100th appearance for his club, was replaced through injury by Joao Pedro.
Sarr almost doubled the lead for the hosts just before the half-time whistle when his volley from a tight angle was turned over the bar by Rudd.
However, the advantage was increased eight minutes after the restart from the penalty spot.
Sarr was upended in the area after a challenge by Jordan Storey and Deeney stepped up to mark his return to the starting line-up with his first goal of the campaign.
The afternoon looked set to get uncomfortable for Watford two minutes after doubling their lead, when a long-range effort by Tom Barkhuizen took a deflection to wrong-foot Foster.
But the two-goal advantage was restored on 59 minutes when a one-two with Deeney saw Nathaniel Chalobah guide the ball past Rudd.
The Preston goalkeeper remained the busier of the two shot-stoppers, saving from Deeney then tipping a Sarr effort over the bar.
The Hornets skipper remained highly involved, although he was guilty of heading over the bar from less than 10 yards out after finding space in the area.
Watford netted their fourth goal on 74 minutes through an unmarked Pedro at the back post and remain unbeaten on home soil this season.