Reijnders struck the opener for City before Omair Hutchinson leveled the scores ahead of Rayan Cherki finding the winner for the visitors.
Reijnders said afterwards: "We know a lot of clubs suffer here. From what I heard Nottingham Forest at home is always difficult, and yes (it's true) I felt it as well. It's a very important win and we are on the hunt.
"They made the spaces really tight so it was very difficult to find the free man in between the lines. In the second half we made some changes to the formation and we could find the free man more often."
On his goal, he said: "I had to play higher on the pitch (in the second half), so they had more difficulties choosing who to get. The goal was a perfect example of this. Of course Cherki knows how to find those passes and I could finish that one. He is very good, he finds spaces and when he gets the ball you have to be ready and in position."
On playing for Pep Guardiola, Reijnders added: "Yes he is very intense but he makes us all better players. For me now I'm here four or five months, you look differently at the game. I want to learn more and more and more."