Late goals from Patrick Agyemang and Rowan Vine saw QPR come from behind for a third consecutive home win.
Relegation-threatened Scunthorpe took the lead on eight minutes with Gavin McCann's curling 20-yard free-kick.
A Martin Rowlands penalty two minutes before half-time put the Hoops level, and in the 79th minute Agyemang fired into the roof of the net from 18 yards.
Vine sealed the win in the fourth minute of injury time with a well-taken finish from 12 yards.
QPR boss Luigi De Canio:
"I didn't think reaching the play-offs was possible before this game and I haven't changed my mind.
"While some might say relegation is not possible either, I know from personal experience that is not yet the case.
"When I was at Siena, we were bottom of Serie A and Bologna in the Uefa Cup places. We stayed up, they went down."
Scunthorpe boss Nigel Adkins:
"It wasn't a penalty.
"We were doing well and then that decision went against us, but I have to be careful what I say.
"It's not the first time that kind of thing has happened to us. We have played good football this season and again a decision has gone against us."
Bookmark with:
What are these?