The 26-year-old slotted the first once a terrible backpass by Christian Oliva and Borja Valero broached in for 2-0.
Lukaku headed in his second, Oliva smitten low to create it 3-1 before Andrea Ranocchia’s header sealed the win.
Lukaku has currently scored eighteen goals in twenty five appearances for the Italian side.
Holders Lazio cruised to a 4-0 finish over Serie B strugglers Cremonese , taly international Ciro Immobile scoring from the spot in the comfortable finish.
And in Tuesday’s alternative match, Lorenzo Insigne scored with 2 penalty kicks as Napoli defeated Perugia 2-0. Napoli’s former Arsenal goalkeeper David Ospina saved a spot-kick from Pietro Iemmello.
League champions and 13-time winners Juventus are at home to Udinese in their last-16 match on Wed.