Cole Palmer had a first-half penalty saved, but Chelsea managed to win thanks to Marc Cucurella's winner on the hour mark.
Afterwards, Maresca said: "This is why I was so happy at the end. They gave everything and were unbelievable. It's not happy when you prepare for one thing and the other team arrives here and it's completely different. Between first and second halves, we created enough to win the game.
"Marc scored a fantastic goal but we had more chances to score a second one. It's not easy for the players because we had to adapt and they did that fantastic.
"Cole is going to miss more penalties in life. From the outside it's hard to understand, he didn't feel well during the night but he wanted to be there to help win the game. With Cole, we are happy with him.
"Sometimes the fans don't understand how difficult it is. We prepared in the last three games in one and Leicester played in a different way. We need 12 players at home and I think we can be there."
The Italian also said: "Don't forget that Leicester against Arsenal for 80 minutes was 0-0. It's not easy. We created enough to be one goal ahead of them.
"The Leicester keeper is brilliant and Cole is going to score more penalties and miss more. He didn't feel well in the night. The people need to understand the effort he made to be there. Cole is a top player. Everything is normal now.
"We have two goalkeepers. The idea is not to change them. We changed in the past but hopefully not in the future.
"We won the game, we are happy. We still have 10 games to go. We are there."