A fine first half display was rewarded when Nacer Chadli slotted home from the penalty spot in the 37th minute but as Mauricio alluded to afterwards, the game changed when Federico Bernardechi's 30-yarder deflected home off Ryan Mason for 1-1 on the hour.
The momentum was certainly with the Serie A side at that point but we held firm and there was one further chance of note each - Dele Alli volleyed over and Gonzalo Rodriguez glanced a header just wide from a corner after Michel Vorm tipped away Mauro Zarate's shot in the final minute.
The tie will now be decided in the second leg at the Lane on Thursday week, February 25.
"We played much better, created chances and dominated the game until we conceded," reflected Mauricio at the Stadio Artemio Franchi.
"After they scored we conceded possession of the ball a little and lost control of game.
"The momentum of a game sometimes changes and the opposition believed more after we conceded. We had control until the 60th minute but after they scored we didn't manage the ball properly.
"In the end though I'm pleased with the performance over the 90 minutes. We're happy we scored and the tie is open."
Mauricio made six changes to the team that started at City on Sunday and added: "It's important to play with the squad, we've a strong squad and to try and fight in every competition you need to use the squad.
"I'm happy with with all the players. It was another big effort and now we must wait for the second leg but first, be ready for Sunday."
We take on Crystal Palace in the fifth round of the FA Cup at the Lane on Sunday (3pm).