Sancho came on at halftime as Chelsea eventually won via an 86th minute goal from Christopher Nkunku.
Maresca later said: "I think we played two different games. I think first half we struggled and second half was much better. The reason why we struggled first half for me was because we didn't win duels, we didn't win second balls and in this stadium against this team first of all you need to show the desire to win the duels and then also the tactical part is important but first of all you need to show that.
"This was the message after 45 minutes to the players that in this kind of games you have to finish the game with your t-shirt dirty because you need to fight. Second half I thought we were much, much better.
"I think we start second half much better and Jadon helped us a lot but what he did tonight is exactly what we expected from him. As I said, I know Jadon very good because I watched him many, many times in the past and I know what he can give us.
"Then also Christoph (Nkunku) was very good and not just because he scored but because he fought without the ball and Jadon was exactly the same. Tosin (Adarabioyo) was very good.
"The performance second half changed completely but we need to learn this kind of things if we want to build something important and we want to win games first of all we need the desire to win games, win duels and to fight together."
On Sancho, he added: "Very happy, very happy for him. He was very good, I think Joao (Felix) was very good and Christoph scored but was also very good. The reason why Christoph in that moment is because I think we were creating chances but we lacked quality inside the box, so the idea to use him as a No.9 was because any ball inside the box we know he is a quality player and he can decide but we are happy with all of them."