The miss by Ronaldo, through on goal with about twenty minutes of the game gone, followed closely by Xabi Alonso's yellow card for a hack on Messi, constituted a turning point in the game. About ten minutes later, Messi dribbled by four players, and threaded his pass to Sanchez for the equalizer. Barca's confidence grew, and well, you know what happened next.
Visca el Barca!
On an unrelated note, this blogger is moving to Barcelona in February of 2012. I hope to get to as many games in person as possible. I'll keep you posted!