The match looked to be 1-1 when freshly exchanged Adnan Januzaj sent the ball into the depth to Portu who received a touch and then lifted the ball over goalkeeper Rui Silva and put 2-1 in the 89th minute.
Portu had also given Sociedad the lead in the middle of the first half.
Alexander Isak was substituted in the middle of the second game. He had a ball in the post just before the victory goal but the situation was relieved for ruff in a previous sitution.