Napoli moved 10 points clear at the top of the standings after snapping Juventus's eight-match Serie A winning streak.
Serie A top scorer Osimhen was instrumental in securing the win for Napoli as he tormented Juve's defence throughout the game, while scoring two goals and providing an assist.
The Nigerian has netted 12 times in Serie A this season.
"Osimhen is such a great striker. I am stunned by the potential he has and excited to see what he’ll do in future," Spalletti told DAZN.
"There were these two or three balls down the touchline and he has the pace, the skill, the courage and physicality to deal with those situations.
"After all, he smashed his face a couple of times because he goes for every ball. He still has remarkable room for improvement."
Spalletti praised the team for their dominant performance.
"It’s a wonderful night because the team played really well and kept the tempo high, which is what we need to do, and above all the crowd provided a great atmosphere," Spalletti said.