Watford gained three vital points in their battle against relegation thanks to a goal from 18-year-old French striker Hameur Bouazza.
The striker who had a two-minute substitute appearance the previous week, was pitched in for his full debut and was rewarded with a goal after 37 minutes.
"That was a real centre-forward's goal. We don't get too many of those," said Watford manager Ray Lewington. "It worked out a very nice debut for the young player." Bouazza was there some eight yards out to turn the ball past the Preston keeper Andy Lonergan after Jack Smith had fired in an off-target shot.
Preston had started brightly with Eddie Lewis forcing Lenny Pidgeley into a good save when he tipped a shot round the post after 17 minutes.
Ricardo Fuller could have done better when he ghosted past three challenges in a fine solo run but did no more than prod the ball straight at the keeper.
Watford had their chances with Scott Fitzgerald seeing one attempted chip deflected wide and then heading off target when presented with a good chance by a pinpoint Neal Ardley cross.
After Bouazza struck in the 37th minute, Preston's Michael Keane hooked a shot straight at Pidgeley.
Although Preston attempted to assert themselves after the break the Hornets created the clearer chances. Fitzgerald again headed wide and later saw an overhead kick saved by Lonergan.
Ardley also had an effort blocked and Lonergan saved from Micah Hyde.
Preston substitute Rob Edwards had a fair chance with his first kick but side-footed the ball straight at the defender without testing the keeper.
Preston survived penalty appeals for challenges in the box on Paul Devlin and Neil Cox but after 80 minutes Watford gained breathing space.
Devlin held off the challenge of Michael Jackson to run onto a long throughball from defender Jerel Ifil and lobbed the keeper for a second goal.