Gerardo Martino has said that Barcelona paid the penalty for complacency in the 3-2 defeat to Valencia at Camp Nou on Saturday.
Pablo Piatti and Daniel Parejo fired los Che into a 2-1 lead after Alexis Sanchez had opened the scoring.
Lionel Messi 54th-minute penalty briefly restored parity for the Catalan giants until Francisco Alcacer's strike five minutes later proved decisive.
"The feeling was that the game was over after 30 minutes and we paid dearly," Martino told a post-match press conference.
"When you can step on your rivals, you have to step on them, finish the game and win."
Martino's men, who went into the gameweek boasting top spot in the Primera Division standings, could slip to as low as third if both Madrid outfits - Real and Atletico - manage victories this evening.
