Leeds won 1-0 via a late penalty for a hand-ball against James Tarkowski and converted by Nmecha.
The summer signing later said: "Amazing. I'm really happy. It was a great first game.
On the penalty, Nmecha also said: "I was mainly hoping it would be given. I was quite calm, I took my breath. I decide before the games where I'd go and yes, I put it there.
"There's always disappointment when you sit on the bench for th first game. It was a good pre-season but I'm happy to score.
"We can achieve more than what people think. we play good football and control the game. games like next week, we won't have as much control. we'll have to dig in.
"Every point counts and wherever we can get a win, we'll take it."
