The Belgium international has been in stunning form for the Italian giants.
He has netted 15 goals and added seven assists in just 22 matches this campaign.
Some Chelsea fans may think Mertens was there to talk about a move to the Blues.
“Napoli star Dries Mertens watched Chelsea v Bournemouth at Stamford Bridge”
But the attacker was at the Bridge to see his former team-mate Nathaniel Chalobah.
The Chelsea ace spent last season on loan at Napoli before returning to play under Antonio Conte this year.
Chalobah posted a message on Instagram saying: “Happy with our win and look at the smile on my face when I saw my bro @driesmertens after the game. Thanks for coming bro. Next stop Napoli to watch you. #NapoliMeetsLondon #alwaysagoodtime.”
Mertens only saw the midfielder make a cameo appearance though.
Chalobah came on as a substitute seven minutes from the end as Chelsea beat Bournemouth 3-0 to maintain their lead at top of the league.