The Frenchman provided the cross for Nelson's first Premier League in the 2-1 win over Liverpool on Wednesday.
And Lacazette said the goal was just rewards for the 20-year-old's hard-work on the training pitch.
Speaking after the game, he said about Nelson: "He is a big talent and does a lot of work behind [the scenes].
"I trust in him, he is working a lot in every training session and today he had the chance to start and I am really happy for him because I think he deserves it."
On the result, Lacazette added: "I am quite happy because we won the game. We started with a bit of fear, we didn't want to take responsibility but afterwards we started trying to play, even if it was Liverpool today."
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