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.
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."
"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."
"We came out of two massive disappointments and the team were a bit nervous but focused at the start. Overall, it was a
