Toney’s 13th goal of the season in the second half proved lucky for Brentford as Rangers, who finished with 10 men, were left searching for their first win at their local rivals since 2003.
Brentford took an early lead with a superb Vitaly Janelt strike from 25 yards before Lyndon Dykes gave the Hoops hope with an equaliser midway through the first half.
But Toney’s glancing near-post header just after the hour mark proved decisive and when Todd Kane saw red for a second booking late on, the hosts closed the game out.
Janelt broke the deadlock with a piledriver into the bottom corner from just outside the area after a quickfire counter-attack. The German, a close-season signing from Bochum, latched onto an intelligent lay-off from Rico Henry to leave keeper Seny Dieng with no chance.
Emiliano Marcondes almost doubled the lead minutes later when he pounced on a poor clearance from the keeper, who made amends with a smart stop low to his right.
But the visitors hit back before the half-hour, Bright Osayi-Samuel bursting down the right to whip in a perfect cross for Dykes to sidefoot into the roof of the net.
Referee Matthew Donohue waved away penalty appeals when Dykes was sent tumbling by a clumsy Mads Bech Sorensen challenge right on the edge of the area.
The defender picked up a yellow as QPR players asked for a red before former Bee Yoann Barbet could only find the side netting with the free-kick.
Ilias Chair stung Bees keeper David Raya’s fingertips with a low dipping drive from distance as the Hoops stretched their hosts.
Rangers should have gone into the break ahead when the industrious Chair slipped in Dykes, only for the big striker to slice his shot well wide with the goal gaping.
Rangers started the second half brightly but it was almost Brentford who took the lead again, only for Toney’s cool finish from Bryan Mbeumo’s cross to be ruled out for offside.
But the striker put that right with the winner just after the hour mark from Marcondes’ free-kick.
Substitute Sergi Canos came close to making an instant impact with a slide-rule pass into the path of fellow sub Marcus Forss only for the Finnish striker to lash his effort over.
At the other end Dominic Ball’s 25-yard strike suffered a similar fate as Rangers began to throw men forward in search of the equaliser.
But the visitors’ task got harder after Kane saw red for a needless foul on Forss with time running out.
There was still time for Toney to almost rub salt in the wounds with an audacious chip that just cleared the bar as Brentford began to exert control of the game.
Sub Saman Ghoddos had the chance to deliver the killer blow in injury time after good work from Toney but blazed over in acres of space.
In the end it did not matter as the bragging rights stayed with Thomas Frank’s side.
Additional reporting by PA.