Damion Stewart's 87th minute header completed a remarkable comeback from being 2-0 down to grab all three points at the death.
QPR were the architects of their own downfall as Gavin Mahon's first-half own goal was doubled by Marcus Tudgay from the penalty spot after Stewart had brought down Leon Clarke.
But Rangers did not give up and Rowan Vine started the comeback before Mahon made up for his earlier error and then Leigertwood made it 3-2 at the death.
In truth QPR had the better of the chances in the first half. Heidar Helguson was put through on three occasions, twice he fired wide and then hit the post.
On 15 minutes Lee Cook swung in a dangerous cross from the left and found Adel Taarabt unmarked in the six-yard box, but the Tottenham loanee fired over the bar.
QPR, who sacked manager Paulo Sousa on Thursday, were looking to end the season on a high but the breaks were not going for them.
Rangers went even closer minutes later when Wayne Routledge was played clean through on goal and dinked the ball over the on-rushing Lee Grant in the Wednesday goal, but he watched as the ball came agonisingly back off the post.
Against the run of play the visitors took the lead in bizarre fashion. Etienne Esajas's inswinging courner was headed into his own goal by QPR skipper Mahon.
The only pressure Mahon seemed to be under was from his own goalkeeper - Radek Cerny - but a lack of communication led to Wednesday taking the lead.
Things got worse for Rangers at the start of the second half when Stewart tangled with Clarke in the box and referee Darren Deadman had no hesitation in pointing to the spot.
Tudgay calmly slotted the ball down the middle of the goal and past Cerny to double Wednesday's advantage.
Rangers were given a glimmer of hope when crowd favourite Rowan Vine - who had missed most of the season with a broken leg - came on to replace Taarabt.
And he took just six minutes to make an impact. Routledge's blistering turn of pace left his marker for dead and his shot across goal could only be parried by Grant into the path of Vine, who tapped the ball home from two yards.
The glimmer of hope became even brighter ten minutes later when Mahon got redemption for his earlier gaffe with a stooping header from a Cook cross at the far post making it 2-2.
But a difficult week off the pitch was made easier with events on it, when Stewart headed home another Cook cross to give Gareth Ainsworth's men all three points in an enthralling encounter.