The Spanish champions appeared to be in for a tough task with the Catalans comfortably leading 3-1 shortly before the final whistle, but Di Maria took advantage of a Victor Valdes howler to make sure the tie is still wide open ahead of Wednesday's return leg.
"We went through different stages in the match. We started well, but then they came back and at 3-1 it looked very difficult. Nevertheless, everything changed with the goal from Di Maria which makes the tie closer," Casillas stated to reporters.
"One of our objectives was to score at Camp Nou and we've done that twice. We are more or less pleased with the result.
"In these types of games there are always controversial moments, emotions and clashes. That's only normal. It's football and everyone is trying their best for the club."
The second leg takes place at the Santiago Bernabeu on Wednesday, August 29.