Barcelona have moved four points behind La Liga leaders Real Madrid as Robert Lewandowski's goal was enough to edge past Alaves.
Pedri played a floated cross into the path of Raphinha and his shot was deflected towards Lewandowski, who reacted quickest to finish at the near post on the hour mark.
Moments earlier, Jesus Owono made a sensational diving save to deny Lamine Yamal, who had struck from the edge of the area.
Yamal crossed for Fermin Lopez at the back post but the Spain international failed to connect with the ball as the hosts were unable to increase their lead.
Barca are now unbeaten in 15 league matches against Alaves - 13 wins and two draws.
Hansi Flick's side remain third in the table, three points behind second-placed Atletico Madrid.
Leaders Real suffered a shock 1-0 defeat away at Espanyol on Saturday and Barca took their opportunity to close the gap at the top.
