Although Alan Irvine's men were the last side to defeat the Hornets in the league, they were very much second best in the attacking department in this contest, but remained organised and had luck on their side when they needed it.
Darius Henderson should certainly have done better with a first-half chance after rounding keeper Andy Lonergan, while Dan Shittu will wonder how his header stayed out after the break.
The home side might also have had a penalty when Tommy Smith was bundled over and when Henderson did manage to get the ball in the back of the net late on, his celebrations were cut short by an offside flag.
However, the visitors also had their moments, not least when Paul McKenna hit the woodwork with a first-half piledriver.
The only surprise about a first half which Watford dominated was their failure to convert it into at least one goal.
It was ironic therefore, that it was the visitors who came closest to score when McKenna's fierce 25-yard drive beat Richard Lee, but rebounded to safety off the angle of post and bar.
Before that chance though, Watford should already have been in front when the lively Jobi McAnuff slid in Henderson. The Hornets striker appeared to have done the hard work after rounding Lonergan, but could only blast into the side-netting from a tight angle.
The Preston keeper then did well to push a low McAnuff shot around his near post and also had to tip over a Smith cross that was threatening to dip beneath his crossbar.
Beside these chances, Nathan Ellington twice wasted free-kicks from good positions and fired another decent opening over the top, while John Eustace also saw a close-range effort blocked after getting on the end of a knockdown from a corner.
The Hornets took their time to get back into an attacking stride after the break, but how they didn't score after 61 minutes was anyone's guess.
Following a McAnuff inswinging corner from the left, Shittu headed down and off the far post and the ball looped back across the goal-line, over Lonergan and Smith and Chris Sedgwick managed to head clear.
The closest Preston came after the break was when Richard Chaplow saw a shot deflected narrowly behind, but the home side thought they had finally made the breakthrough when Ellington's angled effort rebounded off the post and Henderson converted the rebound, but the assistant referee had other ideas.