Ryan Giggs scored on his 999th senior appearance for club and country to help lift Manchester United 15 points above Manchester City with victory over QPR.
The Welshman sealed the win after Rafael's spectacular 20-yard strike had given the visitors a first-half lead.
The young Brazilian also showed his worth in defence when he cleared Chris Samba's header off the line.
QPR improved after the break but Giggs timed his run to tuck in with 10 minutes left and later hit the bar.
A stinging shot from Loic Remy was saved by David De Gea and it had looked like United might have to endure a nervous finish before Giggs's intervention settled the contest.
In the end, there was time for Danny Welbeck and Wayne Rooney to waste further chances, as United inflicted a defeat that leaves QPR rooted to the bottom of the Premier League, seven points from safety.
Manchester City, who face third-placed Chelsea on Sunday, now face a huge task to catch United with 12 games remaining.
The only minor worry for the league leaders was an injury to Robin van Persie as the striker set up Rafael for the opener.
The Dutchman was replaced before half-time after suffering what looked like a hip injury as he fell down a cameraman's bunker behind the goal-line.
The visitors had already threatened through Javier Hernandez's early header before Rafael struck, and QPR were scarcely helping themselves by continually giving the ball away.
It was one such loss of possession that led to the opening goal. Adel Taraabt was dispossessed by Giggs, who fed Van Persie and when Julio Cesar palmed away the Netherlands international's cross, the ball fell to Rafael, who sent his shot into the top corner.
Andros Townsend fought back for QPR, demonstrating some neat skill but unable to find a finishing touch. The hosts then came close to an equaliser when Rafael cleared centre-half Samba's header off the line.
Rafael was turning in a performance to back up Sir Alex Ferguson's recent assessment of the 22-year-old as a maturing presence, and moments later the right-back raced to the other end and provided a floated cross for Van Persie, but the striker's measured volley was tipped away by Cesar.
That was the last meaningful action for Van Persie, who was replaced by Welbeck. But the change did little to disrupt United's dominance - Nemanja Vidic should have done better from Giggs's cross but headed over from six yards out.
Jose Bosingwa, making his first appearance since 8 December following a reported fall-out with QPR boss Harry Redknapp, had a busy afternoon at right-back as United probed down the left through the dangerous Ashley Young.
QPR retained possession better after the break and had chances to equalise when De Gea stopped Remy's strike, before keeping out another Samba header.
But just as the hosts were beginning to build some momentum, Giggs - whose 999 games include 64 for Wales and four for Great Britain in addition to his 931 for United - latched onto Nani's pass to score his 168th club goal and demonstrate yet again his enduring value to United.
Manchester United manager Sir Alex Ferguson: "It was a great result for us. It's another game away so it's important, we are 15 points ahead at the moment.
"It was one of these games where the pitch was lively, the ground was tight. There wasn't a great deal of football in the first half to be honest, it was a display from us which was more about determination, concentration and defending and we got through it."
QPR boss Harry Redknapp: "I thought we were bang in the game, then little right-back hits a 'worldie' - he won't hit another goal like that as long as he plays football.
"He's hit one out of the clouds that's gone in the top corner. Up until then there wasn't a lot in it.
"This leaves us bottom today, but we won't be bottom at the end of the season. I still feel we'll get out of it. You probably think I'm mad, but I don't think I am. Everybody else has written us off, but I haven't. I still feel we have a chance."