Puerto missed a sitter when De Gea could only push a Tiberio Guarente shot into his path before the crowd saluted Ferdinand when he was withdrawn with eight minutes left. An equaliser would have been deserved on the balance of play in the second period but Zaha drilled inches wide after another scintillating run.
Instead, Rabello swivelled to score a third in stoppage time after springing the offside trap with a perfectly-timed run.
It might not have been the right result but United move swiftly on to the Community Shield and the chance of some silverware against Wigan Athletic on Sunday.
United: De Gea; Fabio, Ferdinand (Evans 82), Smalling, Büttner; Valencia (Zaha 65), Cleverley (Jones 46), Anderson (Carrick 65), Kagawa (Giggs 65), Januzaj; Henriquez (Lingard 46). Subs not used: Bebe, M.Keane, Lindegaard.
Sevilla: Beto; Figueiras, Fazio, Pareja (Puerto 56), Moreno; Vitolo (Samperio 71), Kondogbia, Medel (Guarante 81), Perotti; Marin; Bacca (Rabello 78). Subs not used: Navarro, Cala, Maduro, Gameiro, Coke, Rusescu, Julian, Cotan.