Real Sociedad midfielder Esteban Granero claims he promised former team-mate Alvaro Arbeloa that they would beat Barcelona.
A solitary goal after just five minutes from Mikel Oyarzabal was enough for the home side to take all three points at Anoeta on Saturday and blow La Liga's title race wide open with six games to play.
Arbeloa reignited a feud with Gerard Pique after the match when he mocked Barca's defeat by tweeting "How difficult it is to win against 11!" in reference to the Catalans' 2-1 Champions League victory over 10-man Atletico Madrid on Tuesday.
And Granero, who played alongside Arbeloa at Real Madrid, was happy to give his old club a helping hand in their title fight.
"Arbeloa is my friend and I admire him a lot. I had spoken with him 'off the record' and promised him the victory, and we won," he said.
"It's a very important win for us which gives us a huge morale boost and tells us that we can beat great teams like Barca.
"I don't think about whether it will impact La Liga or not, I'm mostly happy to help my team. If it then helps Madrid, that's even better, because Barca have been my great rivals since I was little."
Granero was keen to warn Madrid that they will find life just as difficult when they visit Sociedad on April 30.
"Madrid also have to come to Anoeta and they know we will make it just as difficult," he added.