The Paris Saint-Germain wideman converted from a Bernardo Silva knockdown to double his international tally with less than a quarter of the match played.
Fernandes then headed the Selecao into a deserved two-goal lead, before Guedes added his second with a similar goal 10 minutes into the second half.
Relive how the 90 minutes of action unfolded with Sports Mole's live text coverage below.
PORTUGAL XI: Patricio; Soares, Pepe, Alves, Guerreiro; Carvalho, Moutinho; Bernardo Silva, Fernandes, Guedes; Ronaldo
ALGERIA XI: Salhi; Ferhat, Bensebaini, Mandi, Medjani, Benmoussa; Bentaleb, Boukhanchouche; Mahrez, Slimani, Brahimi