The Blues were 2-0 ahead through Reece James and Enzo Fernandez before Gabriel Pereira struck for the hosts to keep the round of 16 tie in the balance.
Maresca said after the first-leg win: "Yeah, very important for many reasons. For sure because it's away, for sure because it's a knockout game now so you need that. And also for the performance.
"They surprised us because in the last almost three years with this manager, they played two games with a line of five, so we didn't expect that. In the first-half, we controlled the game, we didn't create chances. Also, when we planned the game, we also expected not to create many chances when we have Shim (Mheuka), who is 17-years-old, Ty (George) is 17-years-old; we knew we would struggle a little bit.
"Overall, we deserved to win the game and it's good because we gave chances to all of them to get minutes.
"I watch many games when we face a team, so I watched many games from this season in the Conference League and also in the league. They never played with a line of five. In the last two years, they played two games with a line of five. Tonight they played with a line of five and surprised us.
"Overall, I think we did quite well. They are a very good team, they play very good football, with a good manager, good young players. Very good."
On hosting the second-leg against the Danes, Maresca also said: "Now, 90 minutes is finished - we are happy, we won. We have 90 more minutes against them next week but now the most important thing for us, the main game for us is Sunday's game.
"It's at home; we need our fans for 90 minutes, 100 minutes, behind the team and pushing the team because every game is important from now on. Against Leicester on Sunday, I think we can take one more step for our target to finish in the top four or top five, I don't know. It's important, we need to be together to win on Sunday."
Maresca deployed skipper James in midfield on the night and was rewarded with a goalscoring performance. The Italian admits he was delighted with the shift the fullback turned in.
"He is in a very good mood. He played very good against Aston Villa and again tonight. We know how important he is for us; he is our captain, a fantastic player but we all know the most important thing for Reece is that we need him fit. It is our duty and our target to keep him fit until the end because for sure, he is going to help us.
"Tonight, again, he played very good, scored a goal. He can play in many positions because the good players can play in many positions. At this moment, we are using him as a midfielder and he is doing very well.
"You can ask Reece; when I signed with Chelsea, probably the day after, I sent him a video about seeing him as a midfielder. I see Reece as a midfielder, not now - since day one, before I met him for the first time, he was on holiday. I sent him a clip about him playing as a midfielder.
"I mentioned Reece playing as a midfielder a long time ago. He is playing there now but the good thing is he played this year already as a full-back, as a centre-back and in the central midfielder. The main target for us is to help him be fit all season."