Il Toro have made a modest return to Serie A but sit comfortably in mid-table by virtue of a series of impressive performances on the road.
Napoli, meanwhile, have drifted away from league leaders Juventus as Walter Mazzarri's forward line struggles for goals without the injured Edinson Cavani.
Petrarchi told Tuttosport: "We get results away from home because we enjoy getting into spaces that are left empty.
"Napoli are always fired up and even when they are winning the philosophy is to never give up.
"The Azzurri are, in my opinion, the second-best team in the league, even if they did lose to Atalanta.
"We know we are coming up against an outfit that can punish you at any time."
Petrarchi also confirmed reports the Turin outfit are interested in pursuing a swap deal for Partenopei striker Eduardo Vargas, with Rolando Bianchi the possible makeweight in January.
"A Bianchi-Vargas exchange? It's premature to talk about that now, the Chilean is a good player and Mazzarri knows Rolando well," he added.
"Sure, we were after Vargas in August, I personally asked (Napoli sporting director Riccardo) Bigon if he could join us on loan.
"Napoli decided to hold on to him, hoping they could get a return from the lad out on the pitch.
"Vargas is a player with untapped potential, it's inevitable that you have to stay patient with youngsters.
"At the moment, however, we have other things to address and January is far away."
Mazzarri continues to treat Cavani with kid gloves as the Uruguayan international recovers from injury, but Goran Pandev's fresh ankle problem could see the prolific striker rushed back into action against Torino.
Following defeat at the Stadio Atleti Azzurri d'Italia, Mazzarri told Gazzetta.it: "I've given Cavani carte blanche to play on two occasions but the boy hasn't felt right, hopefully he'll play in the next one."
Juan Camilo Zuniga's participation is also in doubt, with the Colombian winger not likely to be risked before next week's visit of Dnipro in the Europa League.