Inter routed hapless Sassuolo 7-0 for the second season in a row today with Argentine striker Mauro Icardi grabbing a hat-trick and Pablo Daniel Osvaldo scoring twice.
Rafael Benitez's problems at Napoli mounted as they lost 1-0 at home to modest Chievo after Gonzalo Higuain missed a first-half penalty and Maxi Lopez struck early in the second half for the visitors.
Benitez, who took a week off before the match, was already under pressure after Napoli lost their Champions League playoff to Athletic Bilbao.
Stefano Okaka scored a brilliant individual goal to help Sampdoria beat Torino 2-0 and was then told by coach Sinisa Mihajlovic that it was time to make up for wasting "six or seven years" of his career.
Icardi got Inter off to a flying start when he beat Andrea Consigli at the third attempt from Mateo Kovacic's through ball after three minutes.
Kovacic provided a clinical finish for his first Serie A goal and Icardi curled in his second as Inter went 3-0 ahead in half an hour.
Osvaldo, signed on loan from Southampton, turned in a rebound just before halftime and Icardi completed his hat-trick when he scored from a narrow angle from a Kovacic pass in the 53rd minute.
Argentine-born Osvaldo struck again with an easy finish from Fredy Guarin's pass and the Colombian completed the scoring to leave Inter with four points from two games, and no goals conceded.
"Our aim is to always maintain this attitude, determination and aggression on the field," said Inter coach Walter Mazzarri, whose team are under pressure to improve on last season's fifth place. "We need to be fast, move the ball around quickly and not give our opponents the time to think."
Napoli missed a host of chances against Chievo, including a Higuain penalty which was brilliantly saved by Francesco Bardi midway through the first half.
Lopez scored Chievo's winner with an angled drive seconds after Bardi made another good save to deny Juan Camilo Zuniga.
"The fact that we had so many shots on goal shows that we did something right," said Benitez. "We have to improve our finishing. We always seem to have trouble against the smaller teams and today Chievo only had two shots on goal."
Okaka scored the best goal of the day when he ran from the halfway line, held off a challenge from Emiliano Moretti and flew past Kamil Glik before scoring from a tight angle.
"He's good technically and physically strong, but up to now he has done nothing," said Mihajlovic. "He has wasted six or seven years. Now, he has to make up for lost time. He could still become one of Italy's best forwards."
Lazio chalked up their first win when Antonio Candreva volleyed the first, Marco Parolo headed the second and Stefano Mauri completed the scoring from Miroslav Klose's pass in a 3-0 win over promoted Cesena.
Genoa goalkeeper Mattia Perin performaned heroics to earn his team a goaless draw at Fiorentina and Atalanta won 2-1 at Cagliari.