Chelsea needed a free-kick from Reece James in injury-time to earn the point at the Stamford Bridge on Tuesday night.
Maresca said afterwards: "I think first half we completely deserved to win the game. We should have scored three goals. When we conceded in the second half, we dropped. We deserved to win the game when we created so many chances.
"It was one of the best parts of the season in the first half. We were aggressive and the chances we created. We are a bit unlucky in scoring goals. We miss and then we concede. We need to continue. The bad thing as I said is that after the penalty, we drop and there is no reason we need to do that.
"The game was completely in our control and it's something we need to improve.
"I have concerns always even when we are winning matches. This is the Premier League, when you don't create chances and don't score then you have to be more concerned."