While I absolutely hate how Arsenal gave 2 free goals, (I also don't think it's acceptable compared to their performance so far); I wouldn't blame it all on "sloppy defense". Mourinho probably pushed Utd to play a very aggressive tactic, he didn't let Arsenal have any chances. With 3 yellow cards and 13 fouls, every time Arsenal had a chance of a counter-attack, Utd just fouled to break their momentum and keep them from scoring. De Gea also picked up his pace by a mile at the end, basically saving Utd by a thread twice from ending with a 2-3.. I honestly hated the game but there's no denying it was completely Arsenal's fault for both goals on them.