A deflected Wayne Rooney goal secured the victory as Sir Alex Ferguson's side capitalised on Manchester City's loss at Everton earlier on Saturday and now sit just 13 points from winning the title.
Defeat meant there was no quick-fix for Reading following the controversial sacking of Brian McDermott earlier in the week and they are now seven points from safety.
Rio Ferdinand, whose return to the England squad has been a talking point, rolled back the years to turn in another marvellous performance, which included claiming the assist for Rooney's winner in the 21st minute.
Nipping in to intercept Garath McCleary's poor pass, Ferdinand advanced into the open space and nipped round a static Mikele Leigertwood before feeding Rooney just to his left.
The striker took aim and once his shot flicked off Alex Pearce, former Manchester City goalkeeper Stuart Taylor had no chance of keeping it out.
After being thrust into the spotlight following McDermott's shock dismissal earlier in the week, Eamonn Dolan became the 15th manager, including caretakers, to face United in their first Premier League game in charge.
Most have lost. And whilst Dolan was not quite accepting of his fate, he seemed to have settled on a policy of damage limitation despite Reading's position becoming even more perilous due to earlier triumphs for Southampton and Aston Villa.
But Reading should have had a chance to equalise immediately after half-time when Nemanja Vidic shoved Adrian Mariappa over inside the box. Reading appealed for what TV replays showed to be a clear foul but referee Lee Mason was unmoved.
United failed to profit from their good fortune, with Danny Welbeck and Ashley Young going close either side of a wild effort from the out-of-form Robin van Persie that flew out for a throw-in.
Rooney fired over before the final whistle but there was no Reading equaliser to worry about and, as certain as it appears United will end the season as champions, Reading look destined to finish it heading to the Championship.