Jaydon Banel scored a late winner for Derby as they twice came from behind to beat QPR 3-2 and stay in the race for a Sky Bet Championship play-off place.
Harvey Vale put Rangers ahead and Oscar Fraulo levelled with his first Derby goal, before Richard Kone put the west London side back in front with his 10th league goal of the season.
Sondre Langas hauled the Rams level again, and Banel's 88th-minute strike - the youngster's third goal in five matches - secured the points for John Eustace's men.
The winner was scored with QPR down to 10 men after forward Rumarn Burrell, recently back after a three-month absence, went off injured with Rangers having made all their permitted substitutions.
Derby's vital - and rare - away triumph means they will go into the final weekend of the season eighth in the table and with a chance of making the play-offs unless sixth-placed Wrexham beat champions Coventry on Sunday.
They had lost their previous three away matches and six of their past seven on the road.
Rangers, who have now suffered three consecutive defeats and are without a win in five games, went in front after 13 minutes.
Daniel Bennie did well on the right-hand edge of the penalty area, pulling the ball back towards Vale, who created space for a shot with a nice touch and then slotted past Jacob Widell Zetterstrom.
A Rangers goal had been coming. They were on top from the start and had gone close to going ahead when Vale fired the loose ball against the outside of a post after Kone had been denied at point-blank range by Zetterstrom.
Derby equalised out of nothing in the 25th minute after Rangers could only half clear a corner.
Max Johnston's miscued volley fell to Fraulo, who cleverly met a bouncing ball with a side-foot which would probably have been saved by keeper Paul Nardi had it not deflected off Jonathan Varane.
Rangers responded, with Zetterstrom keeping out attempts from Varane and the lively Paul Smyth as Derby came under more pressure.
QPR thought they had regained the lead on the stroke of half-time when Vale's corner sailed into the net, but the goal was disallowed, seemingly for a push by Kieran Morgan on Zetterstrom.
The lead was restored 10 minutes after the interval. Kone, with his back to goal and under pressure from Matt Clarke, showed great persistence to hold off the defender and shoot into the bottom corner.
But Derby hit back with Langas' 76th-minute header from Joe Ward's right-wing free-kick.
And Banel, on as a substitute, won it with a superb goal, cutting in from the left past full-back Kealey Adamson and firing into the far corner of the net.
QPR's Marti Cifuentes:
"I don't know (how we lost). A lot of frustration at the end of the game for us.
"There was pride at the way we played, how we started the game. It was exactly what we needed to do - impose ourselves on the pitch with a lot of intensity, good movement, attack and be very aggressive in the opponents' half.
"We played unbelievable in the first hour. It was probably the best hour of the season for us. But we created a lot of chances and after one hour we had kept the opponent alive, and when that's the case you never know what can happen.
"And then when you play the last 10 or 15 minutes with only 10 players on the pitch, it's more difficult.
"But for the future we need to manage these type of games better and kill them off when we play this well. It's difficult to play better football than we did today."
Derby's John Eustace:
"That was part of the reason for leaving him [Banel] out. I felt both him and David (Ozoh) could give us a really exciting last half an hour," said Eustace.
"The reason for leaving Jaydon and David out was the amount of work they did on Saturday and Tuesday - their numbers were off the scale.
"I felt they could really impact that last half-hour. To get the impact from those two after the numbers they hit on Tuesday was great.
"What I wanted from them when they came on was exactly what I got.
"What a brilliant win. Fantastic. You have to find a way to win at this stage of the season.
"After that first hour we were probably quite fortunate to be level, but then we made some positive changes and were very good.
"It's part of having a good group of players. Over 46 games there are going to be some really hard games and you have to find a way to win - and we certainly did that today."
