Phil Foden was dismissed after 23 minutes at Old Trafford following an altercation with Bruno Fernandes.
Maresca accepts the sending off made the game difficult for his team but says it also made it tough for United in the 199th derby between the two sides.
It was the message he handed to his Blues boys in the dressing room at the break and it worked a treat, with Erling Haaland bagging the winner on the hour mark.
“We had a plan 11 v 11 that after the red card completely changed,” he said.
“The game with 10 men became more difficult for us but also for them, because they are a team that loves to play in transition, they love space in behind but with 10 players we just dropped waiting for them and we didn’t concede any transitions or concede any space behind.
“That’s why I say it became more difficult for us and for them.
“The message at half-time I said to the players was the game was more difficult for us – but also more difficult for them.
“So keep believing we can win the game. Believe, stay in the game and we can win this game.
“To win with 10 men is already special, but it was even more special when it’s a Manchester derby for the fans, for the players and the coaching staff.”
There were two flashpoints in the game – first Phil Foden’s sending off and then the goal given for Erling Haaland after a VAR check.
Maresca gave his verdict on both circumstances in his post-match press conference.
“I think the red card for Phil Foden is a red card. But I also think in the same action it’s a red card for Bruno.
“For the goal, the fourth official told me that Erling was onside and they were just checking the entire action. Nothing more to add on the goal.”
Despite chances to add to our lead, City were nevertheless thankful for the stopping skills of Gianluigi Donnarumma at the death as he kept our Bryan Mbuemo’s goalbound effort with the clock ticking down to full-time.
Maresca was impressed with his fellow Italian.
“Wow,” he added.
“I think it was the only big chance of the game. Big players score at vital moments. Big keepers make big saves at vital moments like Giogio at the end. It was a great save.”
