The Basque side have enjoyed an excellent start to the 2020/21 season with 11 points now picked up from their first six games.
But their performance against Manuel Pellegrini’s side was their most complete showing in the early stages of the campaign.
Portu’s goal just before the break put the visitors in a strong position after the restart as La Real turned on the style.
Captain Mikel Oyarzabal netted from penalty spot on 74 minutes to make the points safe before Adnan Januzaj netted in added time to make it 3-0.
Alguacil’s side kick off their Europa League campaign in midweek with a trip to face Croatian club Rijeka before hosting Huesca in league action next weekend.
La Real then face a tough run of matches before the November international break with home games against Napoli and AZ Alkmaar and league games with Celta Vigo and Granada.
Image via Real Sociedad CF on Twitter