The Belgian has spent the last four seasons with the Partenopei but it has only been during the last year or so that he has come to the fore, having been moved into a central striker role.
Mertens' switch from his more familiar wide position only came about due to an injury to Arkadiusz Milik but he appears to feel at home as a so-called 'false nine'.
The 30-year-old admits he has enjoyed his switch in position and says that Sarri's influence has been key in bringing the best out in him.
"I started as a central midfielder, then I played as a winger," Mertens explained to La Repubblica. "Then I started playing as a centre-forward. I improved initially because of consistency, which because I'd been starting from the bench a lot I hadn't had.
"Sarri's football seems to be tailor-made for me, I like to play the ball on the deck with fast triangles: the strong and distinctive points of Napoli.
"We're speaking the same technical language and we've all grown together."