Real stunned Barca 2-1 at the Nou Camp.
"The Liga title has practically slipped away. The difference in points is large and there are few [points] left. We knew that it would be difficult, especially knowing that they depend on themselves - but we gave it a try," said Iniesta.
"It hurts our soul to not be able to prolong the Liga a little more, but we have to accept it.
"Our only option was to win and they played with that in mind. With a draw, when it looked as though we were fighting for the win, their fast goal slowed us down."