Greenwood grabbed the winning goal, and Matic thinks there is more to come from the club's emerging stars.
He told BT Sport: "It was a hard game. First half we tried to open the game and score a fast goal but they had a solid defence.
"Second half, when you don't score it is more difficult, but we managed it and it is important to start with three points.
"It is good for the young players to have the opportunity to play these games. They have to use that, work hard and get more chances.
"It is great the club give them the chance. I am happy for them. They are young and want to prove they deserve to wear the shirt. They are the future of the club."