Jimmy Kebe looked to have put the home side on course for a routine victory with an early strike but an own goal from Royals goalkeeper Alex McCarthy gave North End hope of a point.
But substitute Hal Robson-Kanu poked in an ugly winner which dampened Preston legend Sir Tom Finney's 89th birthday celebrations.
North End were much improved after the break in front of a special banner hailing Finney - star of three World Cups for England and nearly 500 appearances for Preston - but the late goal leaves them eight points adrift of safety.
At the other end Brian McDermott's side moved into the play-off places by beating Portsmouth on Saturday and will be tough opposition for anyone on current form.
The home side had the first moment of danger when Shane Long flicked an Ian Harte free-kick narrowly wide but that was a rare chance during a tight opening 10 minutes.
Brian Howard forced the first save of the night from Iain Turner with a low shot on the turn from 20 yards before another Harte set-piece deflected just wide.
North End had their moments on the break, with Eddie Johnson and Iain Hume looking lively, but it was the home side dictating play and it was no surprise when they took a 21st-minute lead.
Long tormented emergency right-back Barry Nicholson with a run into the area and when his cross was deflected up and over Turner, Kebe was left with an unmissable header from inside the six-yard box.
Howard was running the show and forced Turner into a good save with a cross-shot from the right though the visitors ended the half on top without creating a clear-cut opening.
Reading captain Ivar Ingimarsson was booked in the opening minutes of the second half for a cynical handball on halfway as Phil Brown's side looked for an early breakthrough.
And they found it in the 52nd minute.
Keith Treacy whipped in a dangerous free-kick from the right which Johnson flicked onto the far post. The ball bounced out onto the back of the unlucky McCarthy and into the net.
The hosts had not got going after the break but Long shot wide before McDermott made a double change.
Mikele Leigertwood and Mathieu Manset came on to lift the home side but it was Preston who nearly scored again.
Another excellent Treacy cross was helped on by Hume and captain Billy Jones was just unable to turn the ball in from close range.
Johnson was then involved at the other end when he blocked Zurab Khizanishvili's effort from close range, with Reading players demanding a penalty for handball.
A corner was given and North End survived.
Harte then rattled the woodwork with a curling strike from 25 yards as Reading piled on the pressure before substitute Robson-Kanu struck with eight minutes remaining.
Turner came for a cross from the left and collided with his own defender, leaving the winger to lob the ball in from close range.