In the 19th minute David Nugent had a tame header saved by Brighton keeper Alan Blayney and Paul McKenna saw a 25-yard right-foot shot from the left channel fly just wide of the right-hand post.
Joe Dolan was booked for Brighton after 26 minutes for a foul on Nugent on the right-wing by-line.
McKenna had another right-foot shot which went wide of the right-hand post before Gary Hart was tricked by Richard Cresswell inside the penalty area. The referee pointed to the penalty spot and gave Hart a straight red card.
Graham Alexander send the keeper the wrong way with a right-foot penalty into the top right-hand corner of the net for his eighth goal of the season and his sixth penalty success.
Chris Sedgwick had a right-foot shot saved by Blayney after 37 minutes as the Lilywhites turned the screw.
Right on half-time Eddie Lewis fired over a left-wing cross and Cresswell slid in right-footed from five yards out to put the ball into the bottom left-hand corner of the net for his 19th goal of the season.
The fourth official signalled one extra minute and Preston when in at 2-0 up at half-time.
In the first minute of the second half Sedgwick had a shot saved by Blayney and Callum Davidson then shot narrowly wide of the right-hand post.
Paul McKenna played a right-foot right-wing cross over to Nugent in the 51st minute and he hit a seven-yard right-foot shot into the bottom right-hand corner of the net to complete the scoring.