Stadio Diego Armando Maradona: Roma registered their third consecutive victory on all fronts as they made short work of Cagliari 4-1 on Sunday, while defending champions Napoli lost 3-1 to Fiorentina on home turf.
Roma had beaten Frosinone last time out in Serie A and were coming off a 4-0 midweek triumph over Servette in the Europa League.
New signing Houssem Aouar sent the Giallorossi ahead in the 19th minute as Leonardo Spinazzola's floated pass set up him to drill home.
The away side quickly rode the momentum as Romelu Lukaku continued his fearsome form to fire home Rick Karsdorp's pass.
Andrea Belotti added another straight after the break as his mazy run made defenders dizzy before finishing with a low strike, while Lukaku got his second from Leandro Paredes' assist.
Nahitan Nandez converted a spot-kick in the dying minutes, which proved to be nothing more than a consolation for Cagliari.
Elsewhere, Napoli saw their domestic winning streak ruined at Stadio Diego Armando Maradona. Victor Osimhen's penalty cancelled out Josip Brekalo's early opener, but the Nigerian's goal was only a temporary balm for the Partenopei, as Giacomo Bonaventura and Nico Gonzalez both scored in the second half to seal the win.
Also on Sunday, Lazio edged past Atalanta in a 3-2 thriller, with Matias Vecino grabbing a last-gasp winner.
In Sunday's other fixtures, Monza dominated Salernitana 3-0, while Frosinone saw off Hellas Verona 2-1.