Both sides had opportunities in an end-to-end first period, but the score remained level at the interval due to some wayward finishing.
Here, Sports Mole dissects the 90 minutes of action between the two Spanish rivals.
On target: 6
On target: 2
Was the result fair?
Usually when Barcelona lose, especially in La Liga, it can be argued that they deserved to take something from the match. Well, that was simply not the case this evening. As expected, the visitors dominated the possession, but Bilbao were the better side at San Mames from start to finish. You got the feeling that the home supporters would have been happy with a point, but it proved to be a famous win inside their new stadium.
Bilbao's impressive start to the season has been built on a unbeaten home record and therefore it will come as no surprise that they were a threat to Barcelona this evening. The hosts had more attempts and indeed created more chances than the Spanish champions during an impressive 90 minutes of football. Their exemplary work-rate was perfectly demonstrated by Gaizka Toquero, who was terrific. Just about everything went right for the home side this evening.
Laboured, dull, disappointing. Those are all words that could be used to describe Barcelona's performance this evening. Granted, they were without a number of key players, including a certain Lionel Messi, but those on the field will be disappointed with their total of just two shots on target. The team has come under criticism for their new approach this season and this result will only further pose more questions. It is back-to-back defeats for the Catalan outfit after they lost at Ajax in the Champions League during the week.
Sports Mole's man of the match
Markel Susaeta: Simply put, Susaeta was outstanding this evening. The Spanish winger gave Barcelona full-backs Adriano and Martin Montoya nightmares as he continued to swap wings during the 90 minutes. It was also his cross that set up Muniain for the only goal of the match, which capped a fine all-round performance from the midfielder.
Biggest gaffe of the match
Why did it take 83 minutes for coach Gerardo Martino to introduce Pedro to proceedings? Barcelona lacked pace, width and invention this evening - something which the Spanish international would have provided had he been given a chance to influence the latter stages. Martino's decision to select Cesc Fabregas as his central attacker will also be called into question.
Overall, Juan Martinez can be pleased with his display this evening. The Spaniard issued just the one yellow card in a low-key first period, but was forced to issue six more as the intensity grew in the second 45 minutes. There were a number of challenges that the official was forced to address, but he got the majority of the decisions correct.
Bilbao: Bilbao face familiar opponents in the Copa del Rey at the weekend when they travel to fellow La Liga side Celta Vigo.
Barcelona: The Spanish champions are in Copa del Rey action on Friday against Segunda Division B side Cartagena.