Well, this is not the start defending champions Barcelona would have wanted in the league.
They went behind for a third game in a row – a Torres volley putting the hosts in front – and never looked like getting into the game. That was until Fati came on.
The 16-year-old made a major difference and marked an excellent appearance with a goal six minutes into the second half.
Arthur – another substitute – also proved influential, curling a wonderful effort into the corner in the 64th minute.
Could Barcelona see it out? They almost did, save for a Pique handball 10 minutes from time.
And after a VAR check, Torres got his second from the penalty spot to make it 2-2.
SUBS: Inaki Pena, Arthur, Moussa Wague, Ivan Rakitic, Samuel Umtiti, Arturo Vidal, Anssumani Fati.
BARCELONA XI (4-3-3): Marc-Andre ter Stegen; Nelson Semedo, Gerard Pique, Clement Lenglet, Jordi Alba; Sergi Roberto, Sergio Busquets; Frenkie de Jong; Carles Perez, Antoine Griezmann, Rafinha.
SUBS: Adrian Lopez, Roberto Ibanez, Sergio Herrera, Juan Villar, Facundo Roncaglia, Darko Brasanac, Jon Moncayola.
OSASUNA XI (4-4-2): Ruben Martinez; Nacho Vidal, Aridane Hernandez, David Garcia, Pervis Estupinan; Roberto Torres, Oier Sanjourjo, Fran Merida, Ruben Garcia; Chimy Avila, Brandon.