Sao Paulo reached the Club World Championship final but were made to work hard by Saudi side Al Ittihan.
Amoroso fired Sao Paulo into Sunday's final
Amoroso put the Brazilians ahead with a deflected shot after 16 minutes but Mohammed Noor bundled in an equaliser.
Amoroso converted Cicinho's cross to restore Sao Paulo's lead and keeper Ceni Rogerio's penalty made it 3-1.
Hamad Al Montashari ensured a thrilling finish with a header but Sao Paulo held on to reach Sunday's final against Liverpool or Deportivo Saprissa.
Al-Ittihad: Zaid, Al Dosari, Kallon, Tukar, Abushgeer, Tcheco, Khariri, Ibraheem, Noor, Falatah, Al Montashari.
Subs: Al Garni, Al Kahtani, Haidar, Fallatah, Hakami, Al Harbi, Al Sadig.
Sao Paulo: Rogerio, Cicinho, Fabao, Edcarlos, Lugano, Junior, Mineiro, Josue, Danilo, Amoroso, Aloisio.
Subs: Grafite, Christian, Alex, Denilson, Fabio Santos, Renan, Donizeti Flavio.
Referee: Alain Sars (France)