Juventus fell to a surprise 3-2 defeat at Sampdoria on Sunday while Benevento remain without a point after 13 matches in Serie A after losing against Sassuolo in stoppage time.
Duvan Zapata, Lucas Torreira and Gian Marco Ferrari put Sampdoria 3-0 up in the second half before Juventus threatened an astonishing stoppage-time comeback with a penalty from Gonzalo Higuain and a strike from Paulo Dybala.
Juve, who take on Barcelona in the Champions League next week, are now four points behind leaders Napoli, who beat AC Milan 2-1 on Saturday.
Sampdoria, meanwhile, moved five points behind Juventus with a game in hand on most other teams.
The champions were without defender Andrea Barzagli and goalkeeper Gianluigi Buffon, who were recovering from the disappointment of Italy's failure to qualify for the World Cup, and Sampdoria made the most of their absences.
Mauro Icardi scored two headers to fuel Inter Milan, who jumped Juventus for second place with a 2-0 win over Atalanta.
Captain Icardi opened the scoring six minutes into the second half at the San Siro when he powerfully met Antonio Candreva's right-wing free kick.
And the Argentina striker claimed his 13th goal of the season nine minutes later, stooping to nod Danilo D'Ambrosio's in-swinging centre into the bottom left corner as Inter made it 13 games without defeat this season.
Benevento again came agonisingly close to claiming their first Serie A point, before a late goal saw them lose 2-1 at home to Sassuolo.
Samuel Armenteros netted in the 65th for Benevento to cancel out Alessandro Matri's opener but the hosts' hopes of getting something from the match were dashed when defender Gaetano Letizia was sent off two minutes later following a second booking.
Benevento clung on and it appeared as if their luck was about to change when Domenico Berardi hit the crossbar with a stoppage-time penalty, but Federico Peluso netted the winner two minutes later. Benevento have no points from their first 13 matches in the top flight and have twice before conceded a stoppage-time winner.
Talented youngster Federico Chiesa celebrated signing a new deal at Fiorentina with a late goal to help La Viola draw 1-1 at SPAL.
Chievo also drew 1-1 at Torino, where home striker Andrea Belotti had his penalty saved.
Elsewhere, new Genoa coach Davide Ballardini had an ideal debut as he steered his side to a 1-0 win at Crotone.
Cagliari won 1-0 at Udinese.
The Associated Press and Press Association contributed to this report.