The win was the third in as many home matches for new manager Paulo Sousa, who, if he keeps making inspired and positive substitutions, will quickly become a fans' favourite.
The Portuguese's team started the brighter and first tested Andy Lonergan in the Preston goal after only two minutes.
Lee Cook, handed a free role behind strikers Heidar Helguson and Patrick Agyemang, fizzed a shot from the edge of the area that Lonergan could only parry.
First to the rebound was Agyemang, who, having not scored since September, would love to have netted against the club he left last January. But Lonergan was quick to charge down the Walthamstow-born forward's shot and the ball was turned wide of the post.
QPR had their tails up and, with Cook pulling the strings, it was no surprise when they took the lead after 16 minutes.
The 26-year-old Cook, whose loan deal from Fulham is set to become permanent in January, was the provider. His delicious cross from the left flank was met by Helguson's head at the far post, and the Iceland international cleverly nodded back to the left of the goal, giving Lonergan no chance.
But having taken the lead and dominated the first 20 minutes, Sousa's team relaxed and the travelling side took advantage of their complacency in the 28th minute.
After finding space on the right-hand side of the QPR box, central midfielder Paul McKenna cleverly clipped over a pass that found Chris Sedgwick, who had sneaked in from his right wing.
The 28-year-old stole in and skilfully steered his header past Radek Cerny, into the bottom right-had corner - his first goal of the season.
Sousa's team showed good resolve and were back in front with 11 minutes of the first half remaining. At the far post the hard-working Agyemang headed Martin Rowlands' corner back across goal where Cook and Helguson were the first to react.
From three yards out the pair managed to bundle the ball into the net, though the goal was attributed to Helguson.
QPR had chances to put the game to bed, but Preston were handed a lifeline in the second half when referee Alan Wiley deemed that Cerny had felled Sean St Ledger in the area, much to the disgust of the home supporters.
Though the ball was running out of the play the former Tottenham stopper did look guilty. Callum Davidson stepped up to crack the ball in to the net - his second spot-kick of the season.
Sousa threw on leading scorer Blackstock with ten minutes remaining and it proved just the tonic. Cook was awarded a free-kick on the left and Rowlands' cross was nodded powerfully into the net by Blackstock, his tenth goal of the campaign.