Chelsea reached the final 5-1 on aggregate after Thursday night's 1-0 win, with 16 year-old Walsh handed a start by Maresca.
The Blues manager later said: "What do you think, you like him? Good, eh? I like Reggie, I love Reggie because he's that kind of player that, in my system, in the way I want to play, it's perfect. You struggle to find players so young. He's 16. And you see how I was asking for the ball, how good he is on the ball.
"Now, for sure, the most important thing for him is that he continues to study, he continues to go. I ask him now, tomorrow he has to go to school. It's important for him, he has to continue on that.
"But for sure, he's a good player. We finished with Reggie '08 (born), Shimmy (Mheuka) and Genesis (Antwi) '07, and Josh (Acheampong) and Tyrique (George) '06. It's second team, it's not even first team, it's second team.
"So it's fantastic for the academy, it's fantastic for Chelsea, it's fantastic for the fans because the future can be important. Good feeling."
Walsh was laughing
On Walsh's reaction to learning he would be starting, Maresca added: "He was happy, he was laughing. He was surprised also because of his personality.
"He was not worried at all, he was laughing.
"I told him you have to play in the same way that you do training session with us. Enjoy, ask for the ball, enjoy. And you can see that he was doing well."