Bradford were reduced to 10 men after 14 minutes when defender Chris Routis was sent off for bringing down the visitors’ leading scorer Joe Garner, who was bearing down on goal as he chased a long headed clearance from Bailey Wright.
Despite being a man short, Bradford had the best first-half chance a minute before the interval when Jon Stead took advantage of a mistake by Preston captain Tom Clarke only to shoot straight at goalkeeper Sam Johnstone.
Preston made the home side pay for that miss a minute after half-time when Gary Liddle fouled Jermaine Beckford in the penalty area and, although Ben Williams saved Paul Gallagher’s spot kick, Gallagher scored from the rebound.
Preston doubled their advantage in the 55th minute as Johnson fired into the top corner from 15 yards after Humphrey had cut the ball back into his path.
Humphrey added a third in the 81st minute with a dipping 25-yard shot.