I only seen the last 15 minutes of the game as I was taking my own training session, but I did see that Celtic where camped in there own half, playing 6 in the back line and another row of 4 and only pressing Utd 30 yards from goal! I cant comment on the rest of the game as I did not see it, but by defending so deep Celtic invited pressure, and it was always set for a shot from long range being parried by the keeper in wet conditions and it then becomes a race to who gets to the 2nd ball(loose ball) quickest.