Jordi Alba scored late on against his former club to salvage a 1-1 draw for Barcelona in the top-of-the-table clash against Valencia, but the match was marred by a hugely controversial decision to not allow a first-half goal, scored by Lionel Messi.
Messi tried his luck with a first-time effort on the edge of the area after half an hour and goalkeeper Neto fumbled the shot, resulting in the ball crossing the line by about half a metre, but referee Ignacio Iglesias Villanueva and his officials failed to spot it, effectively costing Barca two points.
Ernesto Valverde's men produced what was arguably one of their best halves of football so far this season in the first period, as they quickly got to grips with Valencia's intense style and asserted their dominance at Mestalla.
The officials took centre stage with their howler, though, before Barca's misery worsened after the break.
Valencia was significantly more threatening from an attacking perspective in the second half, resulting in Rodrigo turning home from inside the six-yard box.
Barca ensured it returned home with a point, however, as Alba made the most of a sublime Messi pass to keep the club's unbeaten start to the league season, and four-point lead over Valencia, intact, but there will be an undoubted element of frustration over the first-half controversy.