QPR cursed the lack of goal-line technology in the Championship after Conor Washington's header appeared to cross the line from his second-half header - but no goal given.
It got even worse when Rovers' Sam Gallagher converted from eight yards in the first minute of injury time to steal the points from Blackburn.
TV replays showed the ball over from the effort by the Hoops striker, but neither referee Tony Harrington or either assistant had the advantage bestowed on their Premier League colleagues.
In truth, Rangers went from great to OK after a terrific start.
Rangers were out of the traps like greyhounds with Jason Steele the only thing between Jamie Mackie, a Joel Lynch header and a 2-0 lead in the first five minutes.
Then it all went quiet as both sides appeared to settle for a tentative duel rather than an all-out battle.
Rovers had a bit more going from them after the break, and after 53 minutes the in-form Alex Smithies did well to punch away a free-kick in a throng of players.
And then came the big talking point.
Darnell Furlong supplied the cross, Conor Washington's header hit the bar and down and nothing.
Replays showed it was over the line, but ref Tony Harrington and assistants missed it and the stalemate prevailed.
It was almost an injustice compounded when Darragh Lenihan fired goalward from the angle to bring another terrific stop from Smithies.
Connor Mahoney then went close, before James Perch warmed the palms of the Blackburn keeper.
But out of nowhere, Gallagher eased relegation fears for Rovers and left Rangers wringing their hands in frustration.
How well did QPR play today?
1000+ VOTES SO FAR
Keep up to date with the latest news in west London via the free getwestlondon app. You can even set it to receive push notifications for all the breaking news in your area.