But the victory threatened to be overshadowed by United and England forward Danny Welbeck's blatant dive.
Welbeck's controversial move won United an early penalty, missed by Javier Hernandez, although that only delayed the inevitable as the home side scored three times in 15 minutes early in the second half.
Scholes opened their account after 51 minutes when Wigan goalkeeper Ali Al-Habsi could only parry a dangerous, low cross from Nani into the path of the veteran United midfielder who converted into an open net from four yards.
After 63 minutes, Dutch left-back Buttner continued what had already been a promising debut after the Wigan defender Ivan Ramis was caught in possession in his own area by Welbeck.
The ball was played to Ryan Giggs who, in turn, fed Buttner whose low shot was turned in by Hernandez from close range.
Buttner appeared ready to claim that goal but, in any case, only had to wait two more minutes to claim one that was undoubtedly his.
Gathering the ball outside the area, Buttner surged into the Wigan penalty box, casting aside three challenges before somehow forcing the ball into the goal from an impossible-looking angle via Al-Habsi.
The final goal, after 82 minutes, came from Powell, a substitute 11 minutes earlier.
After James McCarthy gifted the ball to Rafael, the full-back's lay-off was met by Powell who beat Al-Habsi convincingly from 18 yards.
It was an occasion for anniversaries at Old Trafford - Giggs became the first player to appear in 600 Premier League games, Scholes made his 700th United appearance in all competitions, while Rio Ferdinand was playing his 400th game for the club.
Perhaps the most significant landmark on Saturday, however, was that manager Alex Ferguson was taking charge of United in an Old Trafford league game for the 500th time.
That win should have been well within Ferguson's grasp after just four minutes when referee Michael Oliver awarded Welbeck and United a contentious penalty.
The England forward chased Nani's through ball and rounded goalkeeper Al-Habsi before going down under the Wigan man's challenge.
Replays showed there had been no contact involved and a degree of justice was done, therefore, when Al-Habsi made a magnificent save from the penalty, diving low to his left to keep out Hernandez's drive.
Nani might have scored from the resulting rebound, also, but Maynor Figueroa showed lightning reflexes to reach the loose ball and clear.
The incident was part of a bright start from the home side, who had rested new signings Robin van Persie and Shinji Kagawa with an eye on the Champions League group game against Galatasaray in midweek.
Inside the opening minute, Nani had worked well down the right with his cross finding Hernandez whose header lacked power or direction from six yards.
But although United were on top, they received a warning about Wigan's potential threat when Arouna Kone got to Figueroa's far-post cross after a slip by Ferdinand, but failed to make clean contact with an attempted volley.
Kone opened the second period with a stooping header which cleared the crossbar but it was a rare moment of optimism as, following Scholes' opening goal, Welbeck almost made it two, miscontrolling a Nani cross but still managing to scoop a shot just wide.
There could have been more goals for the home side, even at 3-0, but substitute van Persie failed to convert Hernandez's 73rd minute cross.
Source: AFP
Source: AFP