Chelsea won 3-1 as David Turnbull canceled out Alejandro Garnacho's first of two goals for Chelsea with Pedro Neto also scoring on the night.
Maresca said afterwards: "Very happy, especially for the effort of the players. I said yesterday that the schedule is full of these tricky games and so you have to pay attention and we did that.
"Off the ball good, on the ball struggled to make chances. Second half much better on the ball.
"It was a big difference between second and first half, the way we attacked, Cardiff were good, organised and intense off the ball. But in the end I think we did enough to win the game.
"An isolated action when they scored, we could have defended better in that moment but they try to attack and score and unfortunately we conceded."
On trusting his substitutes, Maresca also said: "I trust all the players, knowing that sometimes for some it's more difficult. Tonight we had Buonanotte, marci not playing a lot, it's not easy for them but they did a huge effort and we were better on the ball in the second half.
"We are going in the right direction, everything I do is because I want the best for everyone - the fans, players everyone."
On feeling supported at the club after this week's outburst, he added: "Tonight the focus has to be that we reached the semi-final, the support from fans has always been there, overall tonight the focus has to be that we won and we are in the semi-final.
"We are in semi-final, we will wait for tomorrow night to see what the next step is to get to the final and hopefully we can reach the final."