Shane Duffy’s 14th-minute goal put Blackburn ahead at Loftus Road.
Keeper Alex Smithies, making his full league debut for QPR, spilled Craig Conway’s left-wing free-kick at the far post and felt he was fouled by Duffy, who tapped into an unguarded net.
Blackburn had been dealt an early blow when left-back Tommy Spurr was poleaxed as he defended a second-minute corner and was eventually stretchered off after six minutes of being attended to on the pitch.
The inclusion of Smithies, who replaced the suspended Rob Green, was the only change to the Rangers starting line-up from Saturday’s home defeat against Nottingham Forest.
Alejandro Faurlin and Jamie Mackie returned to the QPR squad after their respective injuries and are on the bench.
Subs: Lumley, Hall, Hill, Doughty, Faurlin, Mackie, Gladwin.