Carlos Tevez fires home the match-winning penalty at Old Trafford
Carlos Tevez struck from the penalty spot in the 76th minute as Manchester United edged into the quarter finals of the Carling Cup following a dour match.
The Argentine made no mistake from the spot after substitute Danny Welbeck had been felled by Peter Ramage, but it was far from a vintage United performance.
Ji-Sung Park earlier hit a post but a much-changed United side failed to turn their utter dominance into chances.
QPR defended throughout, though Samuel di Carmine had a late effort ruled out.
The Italian forced home from close range but the official's flag was the right call - and an equaliser would have been unjust given the visitors' reticence to attack.
For their part, United totally dominated possession but - with Wayne Rooney, Dimitar Berbatov and Cristiano Ronaldo rested - attacks constantly misfired.
Still, eight changes to the starting line-up that went down 2-1 to Arsenal at the weekend perhaps explains the disjointed display United produced.
On the day news broke that Owen Hargreaves will be out for the rest of the season with knee trouble, United boss Sir Alex Ferguson will have been pleased to see Rodrigo Possebon pulling the strings in midfield.
But United struggled to create many clear-cut chances, Tevez forcing a fine, low save with a stinging shot before Rangers keeper Radek Cerny almost let in Ji-Sung Park when he spilled Anderson's effort.
Those were the highlights of a largely drab opening half and things barely got better at the start of the second, with Nani, Anderson and Park all guilty of wayward passes.
Park nearly provided the breakthrough on the hour mark, blazing a 30-yard effort against the post after good work by Rafael da Silva and minutes later Tevez forced Cerny to tip over from 12 yards.
QPR finally managed their very first effort on goal on 73 minutes when Dexter Blackstock brought an easy save out of Tomasz Kuszczak.
Three minutes later Nani burst into the box well and laid the ball to Welbeck, who was clearly felled by Ramage.
Tevez, who has regularly been left out of the United starting line-up in recent weeks, made no mistake from the spot, sending Cerny the wrong way.
Rangers finally rallied following the goal and after Di Carmine's effort had been rightly ruled out, Emmanuel Ledesma fired wide of the goal after Blackstock's shot had been saved.
It was commendable effort at the end of the match from the visitors, but few could argue United deserved the win and to go through to the last eight of the competition.
Man Utd boss Sir Alex Ferguson:
"Danny Welbeck changed the game for us, really, and I'm really pleased with him. He gave us something different and earned the all important penalty.
"He's only recently back from a groin injury but now that he's fit he's very much in the first-team picture.
"The only area that has been letting us down of late - and it showed again tonight - is taking our chances. But the goals will come, I'm sure."
QPR caretaker manager Gareth Ainsworth on injuries to Gavin Mahon, Lee Cook and Daniel Parejo:
"They are problems we could do without. I will be making changes on Saturday against Burnley that's for sure.
"We have given a good account of ourselves and this is a fairytale for me.
"But we are back down to earth at Burnley on Saturday. The Championship is important for us. We have massive ambition and we want to get out of it."
Man Utd: Kuszczak, Rafael Da Silva, Neville (Vidic 89), Evans, O'Shea, Gibson, Possebon (Welbeck 72), Anderson, Nani, Tevez, Park.
Subs Not Used: Foster, Carrick, Manucho, Cleverley, Gray.
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