Belgian forward Mertens scored from the penalty spot once Liverpool defender Andy Robertson was judged to own fouled Jose Callejon.
Former Tottenham forward Llorente then capitalised on a slip-up from Virgil van Dijk in stoppage-time to roll the ball past liverpool keeper Adrian.
Jurgen Klopp’s aspect are the primary winners of the competition to lose the gap game of the subsequent campaign since AC Milan in 1994.
Goalkeeper Adrian had earlier created 2 keys saves for Liverpool, who at first struggled to impose themselves within the daunting atmosphere of the San Paolo stadium.
The 32-year-old, deputising for the battle-scarred Alisson, doubly saved from compatriot Fabian Ruiz throughout the primary amount and created an impressive point-blank save from Mertens’ volley simply once the break.
However, in contrast to the corresponding fixture last term, once Liverpool did not register an endeavor heading in the right direction in their 1-0 defeat, Klopp’s aspect did turn out moments of slick football to threaten the hosts.
A flashing Mohamed salah drive was fantastically tipped to safety by Napoli goalkeeper Alex Meret, United Nations agency additionally saved Sadio Mane’s toe-poked shot with the score at 0-0.