Barcelona captain Andres Iniesta admitted his side were struggling to digest their 1-1 draw away to strugglers Las Palmas on Thursday after two big refereeing decisions went against the La Liga leaders.
Match official Antonio Mateu Lahoz did not spot the home side's goalkeeper Leandro Chichizola handling the ball after charging out from his area at the end of the first half, which could have lead to the Argentine being sent off.
The referee further enraged the visitors by awarding Las Palmas a penalty early in the second half after the ball brushed against the arm of Lucas Digne, allowing Jonathan Calleri to cancel out Lionel Messi's ferocious free-kick strike.
The draw leaves Barca only five points ahead of nearest challengers Atletico Madrid before Sunday's title showdown against Diego Simeone's high-flying side at the Nou Camp.
"I've always said a referee has a difficult job but in the first half we clearly saw their goalkeeper commit a handball so the draw leaves us with a bitter taste," Iniesta told reporters.
"Las Palmas did a superb job today and we lacked sharpness in the final third to finish them off. But we are still top of the league even though our lead has been cut down and this result won't change our mentality."
When the final whistle sounded, unused Barca substitute Gerard Pique ran towards the officials in a fit of rage and had to be restrained, while usually level-headed coach Ernesto Valverde lost his cool when Chichizola was let off the hook.
"The penalty came as a shock to us because of how it was awarded," said Valverde.
"We felt that they equalised with an 'invisible' penalty, they grew stronger after that and we played in too much of a hurry."
Midfielder Sergio Busquets added: "We've dropped two points at a very important moment in the season but we knew we were coming to a difficult ground even though they are in the relegation zone.
"Next Sunday against Atletico Madrid will be the hardest battle of all. We're in a privileged position in the league and we're going to try and maintain it with a victory on Sunday."
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