Athletic Bilbao recorded their second straight win as local rivals Osasuna were consigned to a 2-0 defeat.
The hosts took the lead through an own goal by Alejandro Arribas just after the half-hour mark and Oscar De Marcos made sure of the points by netting the second after 82 minutes.
The game was played in the unfamiliar setting of Real Sociedad's stadium Anoeta, as Athletic's Nuevo San Mames ground is still under construction.
Ernesto Valverde's side looked livelier than their opponents from the start and could have scored in the opening minute, when Aritz Aduriz attacked from the left side of the box but his shot ricocheted off Osasuna goalkeeper Andres Fernandez and onto the post.
The Navarrans had their moments, however. Sisi squandered an early opportunity, shooting wide on the rebound after Athletic goalkeeper Iago Herrerin failed to hold onto a shot from Emiliano Armenteros, and the latter nearly scored straight from a corner, with Herrerin snatching the ball on the goal-line.
Athletic broke the deadlock after 32 minutes when Markel Susaeta put in a low cross in the box and Arribas diverted the ball into his own net as he tried to clear.
Ander Herrera failed to convert what would have been a spectacular team goal shortly after the break, dragging his shot wide from 15 yards out with just Fernandez to beat.
Arribas nearly made amends for his own goal midway through the second half, heading a corner just wide after Herrerin misjudged the flight of the cross, while Roberto Torres' long-range effort went inches wide of the post.
Osasuna's search for an equaliser became ever more desperate as the minutes ticked by and they were left vulnerable on the counter as the whole team surged forward.
Ibai Gomez squandered a perfect chance to kill the game off with 12 minutes remaining. Osasuna's players had all committed themselves and the winger ran through on goal, rounded Fernandez 30 yards out, but pondered for too long on the ball and was dispossessed before he could get his shot away.
Four minutes later, De Marcos made sure of the points. Once again, Osasuna were caught outnumbered on the break, and this time Aduriz squared the ball from the left wing to substitute De Marcos, who slammed his shot into the bottom corner.
The result means Athletic are temporarily top of the Primera Division table while Osasuna still have no points, two games into the season.