Preston's David Nugent came off the bench and had an immediate impact to inflict capital punishment on sliding QPR.
Nugent had not been expected to make an appearance after suffering a knee injury during Saturday's home win at Cardiff.
But on the 60 minute mark he replaced Adam Nowland - in the side ahead of loanee striker Jemal Johnson - and scored with his first touch.
Graham Alexander's ball from the right allowed Patrick Agyemang to turn it across to Nugent, who fired impressively into the roof of the net from eight yards.
The goal broke his scoring duck which stretched back to August - a fact which reflected the injury and illness nightmare Nugent has endured over the last three months.
Nugent didn't seem content with just one, and went close to doubling North End's lead twice shortly after putting the visitors in front. First QPR keeper Simon Royce beat him to the ball before, seconds later, Royce saved a 15-yard snap shot.
The three points were assured in the 85th minute when Callum Davidson robbed Marcus Bignot of the ball on the edge of the home side's area before unleashing a confident shot from 18 yards which Royce had no chance of saving.
For North End, it was a win which stretches their unbeaten run to nine games - but it could all have been so different.
Lee Cook forced a fine save from Carlo Nash in the third minute, before Shabazz Baidoo's attempt was saved on the line by Nash after Chris Lucketti failed to clear the ball.
And Baidoo thought he'd scored in the 15th minute but his effort was cancelled out after ref Dermot Gallagher deemed the youngster had used his shoulder.
Baidoo then tested Nash on 30 minutes, but the keeper managed to push the ball away.
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