Visiting Barca took an early two-goal lead at the Anoeta, only to ship three goals, including a stoppage-time winner from Imanol Agirretxe.
However, rather than criticising his team for giving up their advantage, Vilvnova instead praised Sociedad for the way that they battled back.
"Credit to Real Sociedad," Vilanova told reporters. "Their win is more due to their merit, rather than us not playing well. I have nothing to reproach the players for."
Despite the defeat, Barca remain top of the La Liga table by 11 points.