#2 Olympiacos didn't park the bus, they were forced to

With Barcelona making quick inroads into the Olympiacos' half, their manager Panagiotis Lemonis deployed them in a 4-5-1 formation in an attempt to thwart Barca's attacks.
Unfortunately, it did not work. Their positioning was off and it allowed Messi to play the role of destroyer in his new (old) false nine role. The Argentine forward managed to find space between the lines and this also allowed him to bring others into the game as he drew Olympiacos defenders out of their positions.
The 4-5-1 was not as compact as Lemonis would have liked and this also allowed Deulofeu to find a lot of space on the right.

As the defence sat deeper with the midfield line also dropping deep, it allowed Sergio Busquets to control the direction of attack by spraying passes from the middle while Paulinho had more freedom to make runs into the box.
The Brazilian almost go on the score sheet twice too, if not for the offside flag preventing him from celebrating what would have been his third goal in a Barcelona shirt while another header came off the woodwork.