Rafael's wonderful first-half drive and Giggs' strike 10 minutes from time helped United secure a comfortable 2-0 away victory over the bottom club.
"One goal is never enough, as you know. It only takes a second to lose a goal," Ferguson told MUTV. "I thought we played much better in the second half, I must say. We created some good chances but obviously Ryan's goal with 11 or 12 minutes to go killed the game."
The Red Devils are now 15 points clear at the top of the standings, although Manchester City could narrow that gap against Chelsea on Sunday. That is not something of concern to Ferguson, though. He was just pleased with another win and another clean sheet, which edges United even closer to a 20th title.
"Yeah, it is a good position but you know the way we approach it is to win our next game," he added on MUTV. "That is the best way to do it, carry on doing that. I think it was more about determination and concentration at the back, in particular.
"We defended that part very, very well. It was a scrappy game at times and the pitch was lively. It is a tight ground and it was an ideal situation for a shock. Fortunately, we didn't get that."
The only negative was an injury to talisman Robin van Persie. The Netherlands international, whose 19 Premier League goals is as many as QPR have scored altogether this season, had to be replaced late in the first half due to a hip complaint.
"He collided with a camera," Ferguson explained. "It seems he hit the base of it and he has got a very bruised hip."
Van Persie's substitution came moments after he forced Julio Cesar into a wonderful save from an equally-impressive volley. The striker latched onto a superb ball from Rafael, who had just cleared a Christopher Samba header off the line and netted a superb opener.
"I said to him he must have closed his eyes," Ferguson said with a smile when asked about Rafael's goal. "He has three goals for us this season. The lad has had an absolutely magnificent season and is maturing all the time. He has had a fantastic game."