Robert Lewandowski got off the mark for Barcelona with a double as Ansu Fati starred as a substitute in a 4-1 victory over Real Sociedad on Sunday, while Villarreal won at Atletico Madrid.
Poland striker Lewandowski, celebrating his 34th birthday, put Barca ahead inside 50 seconds before Alexander Isak levelled for La Real in San Sebastian.
But Fati came off the bench to create goals for Ousmane Dembele and Lewandowski, before completing the scoring himself. Barca's first win of the season followed a disappointing goalless draw at home to Rayo Vallecano on the opening weekend.
Coach Xavi had called for "patience" from supporters after a summer spending spree which saw Lewandowski, Raphinha, Andreas Christensen and Franck Kessie all move to the Camp Nou.