The Aquile were beaten by Henrikh Mkhitaryan and Pedro strikes.
Fonseca said, “We'll be honest, what changed was the first leg in Manchester. I thought we would take a few more risks in the second leg, we played well then and the next games, so there was no reason to change when we had found some form.
“I think we improved also with the arrival of Darboe. He is young, with such courage, always looking forward and he helped the whole team to improve by changing the balance. The system change made a difference, but to be perfectly honest, this young lad made the difference too. It's rare to find someone so young who is so confident and calm on the ball.
“With an extra man in midfield, the team feels more comfortable and Darboe provides some defensive protection. We were also focused throughout and made no errors. We obviously wish we'd had that focus throughout the season, but this is not the time for regret.
“We want to celebrate this victory in the derby."