The victory put United 15 points clear of champions Manchester City who faced third-placed Chelsea at home on Sunday.
Arsenal ended a difficult week following home defeats by Blackburn Rovers in the FA Cup and Bayern Munich in the Champions League by beating Aston Villa 2-1 with two goals from Santi Cazorla to move within a point of fourth-placed Tottenham Hotspur, who face West Ham United on Monday.
Wigan Athletic improved their chances of avoiding the drop when they won 3-0 at fellow strugglers Reading and moved above them and Villa and out of the relegation zone.
United, who last lost at Loftus Road in the old first division in May 1989, went ahead there when Rafael blasted an unstoppable 30-metre shot past his fellow Brazilian, goalkeeper Julio Cesar, in the 23rd minute.
Giggs, playing in his 999th senior match, made it 2-0 to Sir Alex Ferguson's side 10 minutes from time when he sent the goalkeeper the wrong way.
Ferguson was full of praise for his side, especially the two scorers, telling Sky Sports: "We got a fantastic goal to set us up to make sure we were going to be hard to beat.
"It was a great strike from Rafa who has made a great contribution. His form this season has been wonderful and we are very pleased with him."
He told the BBC: "Ryan scored at a crucial time - he's delivered again - he's an amazing man."
The only worry for United was a hip injury sustained by Robin van Persie, who hurt himself after tumbling into a TV camera dugout and was substituted in the first half.
"It will be sore for a few days, but hopefully he will be fine for the Real Madrid match," Ferguson said referring to the Champions League last 16 second leg match at Old Trafford on March 5.
QPR manager Harry Redknapp, whose side are seven points from safety with 11 games left, added: "They are a top team and that is why they are going to win the title, they are the best team.
"We have only scored 19 goals in the league all season and that is not going to keep you up.
"There were positives. Loic Remy looked like he was getting over his injury and showed some flashes. If we can get Bobby Zamora fit again, I think we will be OK.
"I think as a pair they can score a few goals for us."
Across London, Arsenal ended their run of two successive home defeats with their win over Villa thanks to a double from Cazorla with the first coming six minutes from the start and the winner five minutes from the end.
In between, Andreas Weimann equalised for Villa after 68 minutes.
Arsenal manager Arsene Wenger was a relieved man.
"We came out of two massive disappointments and the team were a bit nervous but focused at the start. Overall, it was a
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