The former Arsenal man, who was making his 12th league appearance for the Catalan club this season, struggled to defend an inswinging cross just past the half-hour mark and ended up heading it past Victor Valdes to give the hosts the lead.
Lionel Messi then hit back for Barca just four minutes later - but second-half strikes from Antoine Griezmann and Zurutuza sealed victory for Sociedad.
Manchester City fans might just be looking on with glee as they cling on to the hope that they can still knock Barcelona out of the Champions League.
And they may also be pleased to know that Barca boss Gerardo Martino was sent to the stands during the defeat to fifth-placed Sociedad, a loss which leaves the Catalans three points off new league-leaders Real Madrid.
City find themselves 2-0 down after the first leg of their last-16 tie in Europe but a 3-1 win would take them through to the quarter-finals.
And maybe a shock win might just be on the cards if Song makes the starting line-up. Especially if he makes a habit of finding the wrong net with such precision.
image: © mariosp