Enzo Fernandez had Chelsea ahead early before Marco Asensio's brace for Villa saw the hosts to victory on Saturday night.
"Even after the 1-1, we had chances to score," Marseca said.
"We had some great chances and in this league you have to be clinical otherwise until the end anything can happen.
"I think it is the dynamic of the game. There are moments you are more in control and you create chances, and then there are moments they do the same. You have to manage both. This is why we have said many times that the difference is inside both boxes."
Cole Palmer fluffed a late chance for Chelsea and Maresca said: "Cole is a top player. Top players always want to win and play an important part but today he could not. He has some great chances that he missed but nothing changes. We are very happy with him.
"We expect exactly what he can give us but I said many times we cannot rely on him for every game, We need all the team. Today was good but unfortunately we lost. We hate to lose but this is a bad moment."