Madrid's 33-match unbeaten run appeared to be set to come to an end following Luis Suarez's opener, but Sergio Ramos powered in a header from Modric's free-kick in the 90th minute to preserve Madrid's six-point lead at the top of La Liga.
"It is a hugely important and deserved point. We fought right up till the end and we never gave up," the Croatia international told the club's official website.
"We played well, especially in the first half. They were more dominant in the second half and they went ahead, but we never gave up and a goal like that in the Clasico feels like a win.
"It is vital that we remain leaders and we do not let up, we must continue in the same way we have until now.
"We are on a very good run of form and are playing with confidence.
"Going 33 games unbeaten is no coincidence. With the quality and the world-class players we have, if we play as a team, giving everything out on the pitch, we are very difficult to beat."