The 19-year-old came off the bench early on to replace his fellow Manchester City loanee Brandon Barker.
Nmecha initially played on the right-hand side of North End’s attack before switching into a more familiar striker’s role when matchwinner Louis Moult went off.
He certainly caught the eye at the City Ground, tracking back when playing in the wide role and then holding the ball up well later in the game as PNE defended their lead.
Lilywhites manager Neil said: “Lukas is a young lad who is finding his way.
“He had loads going for him and the time in the second half on Saturday when he turned Jack Robinson and got away from him just showed what tremendous pace he has.
“For Lukas, it is just about putting his game together.
“It is about doing the ugly bits of the game which your team needs sometimes.
“You’ve got to pin people, take the ball in, win fouls, run the channels.
“Lukas had to put in a man’s performance at Forest and he did that.
“He’s a good lad, he wants to learn and get better.
“Saturday was a very good learning curve for him, you’ve got to remember he’s only 19.”
The only thing missing from Nmecha’s game in a North End shirt are goals.
He had yet to find the net in 10 starts and nine appearances off the bench.
But Neil is confident that the goals will come for the youngster.
“He is the type of player that once he gets his first goal, more will follow,” said Neil.
“Lukas is a good finisher off either foot, he’s powerful and it is just a case of him knowing when to do certain things. He can do it all, it is about when to do it – that will come for him with games.”
PNE are low on numbers in the forward line.
When Barker limped off, the frontline was Nmecha and Tom Barkhuizen either side of Moult.
In the 73rd minute, Moult gave way to Ryan Ledson as Neil sought to shore up the midfield and protect the lead.
That was when Nmecha moved into the middle.
During stoppage time, Graham Burke came off the bench for Daniel Johnson and played on the right.
That left three defenders on the bench as the unused outfield substitutes.
Neil said: “We are down to the bare bones in that area.
“Graham Burke is a No.10, not really one to play off the flank or up front.”
Meanwhile, North End’s Under-18s have landed a home tie against the winners of Port Vale and Norwich in the fourth round of the FA Youth Cup.