Mohamed Rayhi tried to drill the ball in from range for the visitors shortly before the interval, but he just missed the top scorer, allowing Willem II to break down the other end, but Erik Falkenburg's volley was saved.
The hosts were on the front foot again early in the second half, with Nick van der Velden trying to flick the ball on for Falkenburg, but the midfielder's finish did not trouble the goalkeeper.
However, it was NEC who broke the deadlock against the run of play with just over an hour played, as Foor created some space on the edge of the box, curling the ball into the top corner.
Marcel Ritzmaier tried to put the win beyond doubt for the visitors inside the final 10 minutes, running at Lamprou after beating the last defender, but the Willem II keeper made the save.
Funso Ojo pushed for an equaliser down the other end a couple of moments later, but his long-range drive drifted away from the target.
The result leaves NEC sixth in the table, while Willem II stay 14th, having failed to secure a win in their opening four matches of the season.