"We had the usual system but I decided to put Adrian on the right wing to create problems for Cristian Sapunaru, who is not left-back," Simeone told reporters at a press conference.
"That imbalanced the team, though, and they had more people in the middle of the field when there was a second ball.
"Then, with a 4-4-2, we were stronger, more together and that made us more dangerous. Diego gave us more depth in midfield while Sosa did very well with the corner that made it 1-0."
Atletico are in Champions League semi-final action against Chelsea next week.