Chelsea's goalscorer were Joao Felix (2), Christopher Nkunku (2), Marc Guiu, Axel Disasi, Tosin Adarabioyo and Mykhailo Mudryk on the night.
Maresca later said: "I think the players showed how professional and serious they are. It is very easy to sleep in these kind of games. Football is full of surprises. It was to show how serious we are, how professional. They showed that and it's an important message for all of us.
"We have to be serious. It's never easy. Football is full of surprise. If you are not ready mentally, you can sleep against any team. We are professional.
"In the first five minutes, we conceded a chance. You have to be focused. The way to show respect to them, don't underestimate them. Football is full of these kind of surprises. We don't need that."