The Premiership leaders have now beaten second from bottom Charlton in their last nine league meetings.
Charlton's last win at Old Trafford was over 20 years ago and, although they had their moments, they were as likely to improve on that statistic as a snow-ball is to survive in hell.
Once Ji-Sung Park had headed United into a 24th minute lead, Charlton were always up against it and Darren Fletcher's header eight minutes from time gave the scoreline a more realistic look.
Yet Charlton manager Alan Pardew will not be too down-hearted about the result as he surveys his side's chances of Premiership survival.
Defeats by Chelsea and United in the last two games are no surprise for most Premiership teams and at least Charlton now have a more solid look about them.
United were more the artisans than the aristocrats in their latest victory.
They missed the fleet-footed Cristiano Ronaldo, out with a heavy cold, and of United's big guns in attack, only Wayne Rooney showed anything like his normal form.
United had two good early chances - the first coming when Park surged through the middle to hit a ferocious 25-yard drive which was well-tipped over by Charlton goalkeeper Scott Carson.
Louis Saha, out for the last six games through injury, directed a weak header at Carson from Ryan Giggs' fine right-wing cross seconds later.
Charlton's best chance of the game came in the 12th minute.
Osei Sankofa's cross to the near post from the right was met by Darren Ambrose, whose header from six yards out was brilliantly tipped behind one-handed by United goalkeeper Tomasz Kuszczak at full-stretch.
Ambrose tested Kuszczak again with a snap 20-yard shot after 23 minutes, but United were ahead within a minute.
Patrice Evra beat Sankofa as he raced down the left to produce a pin-point cross into the centre of the box which was headed home by Park six yards out.
Rooney produced a sublime piece of skill in the 38th minute. Giggs found the England man on the edge of the Charlton penalty area.
Rooney, surrounded by Souleymane Diawara and Ben Thatcher took both of them out of the game as he flicked the ball up and then took it down, before firing his shot narrowly wide from eight yards.
United lapsed into a spell of complacency at the start of the second half.
Giggs shot wide when well placed and Saha toe-poked a shot from the edge of the box which was taken at full stretch by Carson.
Charlton were a whisker away from a 76th minute equaliser when Dennis Rommedahl's powerful 30-yard free-kick fizzed inches wide off the head of United defender Gary Neville.
Saha shot straight at Carson, but any outside hopes of a Charlton recovery died six minutes later.
Fletcher found Rooney on the left side of the Charlton box and, although Carson blocked his shot with his legs, Rooney was quickest to react.
Looking up, he calmly scooped his cross to the far post where Fletcher scored with a diving header from six yards.
Fletcher was denied by Carson in the last minute, but 3-0 would have been grossly unfair to Charlton.