The Nigerian tapped home to put City 2-0 up before halftime.
After the 2-1 win, Kelechi stated: "It means a whole lot to me, it's a dream come true to play in the Manchester derby and score the winning goal.
"My team really worked hard. Being in the right place at the tight time.
"I didn't think the shot would hit the post but I'm happy it came off me."