Joss, the red card didn't change the game, the play was heading in the same direction was the entire game - towards the Arsenal goal.
What the red card did do was give Arsenal no hope of mounting any sort of attack as they had no outlet. Not that they were allowed to attack before the sending off, when Arsenal got the ball eventually they were forced to give it away because of the constant pressure from the Barca players.
lame. red card for wrong descion and to an influential player is a BIG thing