Three consecutive wins had reignited QPR’s bid for an unlikely play-off place but they were frustrated in a drab first half.
Preston, who are now 14th, 10 points outside the top six, had the better of the opening 45 minutes as Alfie Devine saw a shot from 25 yards out deflected narrowly wide.
Devine then set up Ben Whiteman just outside the area but he pulled his shot over the bar.
It was Devine involved again as North End took the lead shortly after the restart.
His ball to the right-hand side of the area found Potts who shot low back across goal and found the bottom-left corner.
It looked like being the winner until Small bizarrely looked to clear from his own area with his right-boot and somehow sliced over Preston goalkeeper Daniel Iversen and into his own net.
Iversen was then needed to tip Daniel Bennie’s header over the crossbar.
And he was needed again in the final minute of seven added on as he kept out a even better header by Bennie.