Whatever happens tonight, Arsenal will be knackered on saturday. Which can only be a good thing for United.
That's a ridiculous red card, but it's hard to argue Arsenal deserve anything from this game. Barca have had twice as much possession, and Arsenal haven't had a single shot on goal in the entire 90 minutes. I don't think I've ever seen that happen before in a game. Even when Chelsea parked the ocean liner at the Camp Nou in 2009 they at least managed to create 3 chances.