Erling Haaland scored both goals as the Citizens became the first team to win at the Estádio do Dragao in 2026.
Despite the hostile atmosphere, the visitors restricted Porto to no shots on target and threatened to add more before Haaland’s stoppage-time second.
“It was the complete performance on the ball and off the ball for 95 minutes,” Maresca said.
“We created enough chances to win the game in the first half and their goalkeeper was very good.
“We tried to continue in the second half in the same way.
“It’s game by game. It’s a different competition, different stadium but the most important thing is we show who we are.
“We try to be aggressive off the ball and on the ball try to plan how we can win the game.
“In terms of where we are, I don’t know. I can see game after game, the team is improving.”