A stroke of luck helped the forward hand the Red Devils the lead in a poor first half, before they were able to hold on to the win after the break without moving through the gears
Wayne Rooney opened the scoring after 20 minutes but the Red Devils failed to kick on against the Royals in a less-than-entertaining first period.
And the below-par display continued after the break as both sides failed to threaten, leaving Sir Alex Ferguson's men to take full advantage of Manchester City's loss to Everton while their managerless opponents remain in deep trouble at the bottom.
Rooney, Robin van Persie and Danny Welbeck all started for the hosts in an attacking line-up, while Nani missed out due to a hamstring injury and Alexander Buttner replaced Patrice Evra at the back.
Stuart Taylor continued in goal for the Royals, who were under the control of caretaker boss Eamonn Dolan after Brian McDermott's sacking, while Pavel Pogrebnyak was left out despite being available after a three-match ban.
After a sluggish opening 15 minutes, Ashley Young collected a fine ball from Rio Ferdinand before flashing a shot narrowly wide of the post in the first half-chance of the clash.
And the centre-back was again heavily involved as United got the breakthrough with 20 minutes played. Ferdinand expertly carried the ball out from the back and found Rooney, whose strike deflected off Alex Pearce and looped over Taylor.
Welbeck then dragged a shot wide, with Rooney and Van Persie sending long-range efforts into the goalkeeper's arms, as the hosts comfortably dominated possesion but failed to create any clear chances against a stubborn Royals defence.
Hal Robson-Kanu was inches away from an equaliser with a superb, curling left-footed effort from outside the United box, but the score remained 1-0 at the half-time whistle.
Reading started the second period much brighter and were unfortunate not to be awarded a penalty when Nemanja Vidic shoved Adrian Mariappa to the floor in the box.
However they struggled to create any chances of note as the match became scrappy, with both sides allowing sloppiness to creep into their already lacklustre play.
The Red Devils finally sprung back into action after the hour mark as Welbeck had a strike deflected wide and Van Persie and Young saw efforts rise over the bar.
Taylor then palmed away a powerful Van Persie free-kick but the mild spell of pressure lasted for only a matter of minutes before the match returned to its former uninspiring standard.
Reading offered little in attack as they searched for another late goal, and it was in fact the hosts who went closest to a second through a Rooney piledriver and a neat effort from Giggs in the last five minutes.
Van Persie then also shot acrobatically over the bar very late on as the hosts held firm to grind out another win that puts even more space between themselves and rivals City.