Betis had the lead through Ez Abde, before Chelsea stormed back to win through goals from Enzo Fernandez, Nicolas Jackson, Jadon Sancho and Moises Caicedo all after halftime.
Maresca said afterwards: "I am very happy. I was a little bit frustrated in the first half because I think we approached the game in the wrong way. Also I expected a little bit, the happiness was a bit too much after Nottingham Forest because you go all season waiting and waiting. So we struggled a bit first half, second half we were much better and now we are very happy.
"The message after Nottingham Forest was, 'Guys if we want to be an important team then what we have done is done and we have to win the final.' But it's the happiness, the tiredness because we had 48 hours less than them, they played on Friday for nothing, we played on Sunday for a big, big target. So I expected it a little bit.
"In the second half we played much better."
Sancho future and James management
He also said: "We are going to try again. Now we enjoy a little bit for one week, ten days, and then we start again."
On Manchester United loanee Sancho's future: "I said yesterday in the press conference. From now on we are going to sit with the club and decide what happens for next year.
"If we finish fourth it is also because of Jadon, if we win tonight it is also because of Jadon. It is normal in a season to go a little bit up and down, it is part of the game."
Meanwhile, Maresca also explained starting skipper Reece James on the bench.
"I am trying to protect him," he added.