Macheda, who endured a goalless six-month loan spell at Sampdoria last season, could yet be loaned out again by Sir Alex Ferguson this season with the United manager keen for the 19-year-old to gain more experience away from Old Trafford.
But after seeing Wayne Rooney and Dimitar Berbatov both miss clear chances to score in the first-half at the Gillette Stadium, the stunning home of NFL giants New England Patriots, goals by Macheda and Michael Owen ensured a winning start for United on their five-game tour of the United States.
Ji-sung Park's close range goal from Ryan Giggs's pass on 80 minutes stretched United's winning margin further in front of 51,523 spectators - a record attendance for a soccer game at the stadium.
Manchester United (4-4-2): Lindegaard; Rafael, Evans, Vidic (Ferdinand, 46), Fabio; Nani (Giggs, 67), Carrick (Park, 75), Anderson (Diouf, 75), Young (Obertan, 67); Berbatov (Macheda, 46), Rooney (Owen, 46). Subs: Johnstone (g).