Juventus slumped to another surprise defeat on Wednesday when the champions lost 1-0 at Sassuolo while AS Roma reclaimed top spot in Serie A with a 3-1 home victory over Udinese.
Two points behind Roma are Fiorentina, who beat Verona 2-0, and Napoli, 2-0 winners over Palermo.
Inter Milan are level with Fiorentina and Napoli after defeating Bologna 1-0 on Tuesday.
Juve's three-game unbeaten streak was wrecked by a first-half goal from Nicola Sansone.
The visitors were without several key players and conceded in the 20th minute following an exquisite free kick by Sansone.
Things got worse for Juve before halftime when a frustrated Giorgio Chiellini earned himself a second yellow card for hacking down Domenico Berardi.
Defeat left the 'Old Lady' in 12th place with 12 points from 10 matches. Sassuolo are fifth with 18 points.
Roma opened the scoring against Udinese after four minutes when Miralem Pjanic met Maicon's cross with a precise right-foot shot.
Maicon doubled the lead five minutes later as he picked up a back-heeled pass from Edin Dzeko before tearing into the box and beating Orestis Karnezis.
Gervinho added a third in the 63rd minute, his sixth goal in his last seven matches, after collecting Kostas Manolas’ cross in the box and burying the ball beyond Karnezis.
Cyril Thereau pulled one back for Udinese late on.
Roma have 23 points but face a sterner test this weekend when they meet Inter.
Napoli claimed their fifth win in a row after fine goals from Gonzalo Higuain and Dries Mertens sank Palermo.
Fiorentina downed Verona courtesy of a Rafael Marquez own goal and Nikola Kalinic's sixth league strike of the season.
Lazio lost 2-1 at Atalanta as a Dusan Basta own goal and an Alejandro Gomez effort cancelled out Lucas Biglia’s opener while AC Milan beat Chievo with Luca Antonelli scoring the only goal of the game.
An injury-time goal from Diego Laxalt, his second of the match, earned Genoa a 3-3 draw at Torino and Paolo Sammarco's 91st-minute winner gave Frosinone a 2-1 triumph over rock bottom Carpi.
Frosinone and Carpi both finished the game with 10 men.
