Ac milan played openly, sometimes they were too busy attacking and were not ready when there was a counterattack. Ac milan has a big advantage in this match because they are playing at home and are also superior in number of players. The current score was 3-2 where Prague was able to reduce the deficit in the second half. I think Ac milan should be able to take advantage of the situation to continue scoring goals because in terms of play they are able to dominate it well.
I don't see they are playing too openly. They just forget to focus on their defense, they are too busy attacking. 
It is funny that AC Milan conceded a goal again, it was already 2 conceded goals. Although they already scored 3 goals, it will be nothing if Prague scores again a goal. It can be 3 goals made by Prague if AC Milan defenders play carelessly.
And AC Milan played too much on the wings, maybe that was one of their strategies but it worked, plus Slavia Prague only played with 10 players and they had to take advantage of it.