Napoli were held 1-1 at home by newly-promoted Sassuolo, who picked up their first point of the season after being thrashed 7-0 by Inter on Sunday.
Blerim Dzemaili gave the Partenopei an early lead, with home fans expecting an ensuing victory with ease, but the visitors surprised when Simone Zaza equalised six minutes later.
Rafa Benitez's men were unable to find a winner in the remainder of the match and, as a result, lost the 100 per cent record that they had held until this point of the season.
Roma took advantage of Napoli's dropped points to go top of the table outright for the first time this campaign with a 2-0 win over Sampdoria.
Second-half goals from Mehdi Benatia and Gervinho handed Roma their fifth straight win - the first time the club has achieved such a feat at the start of a season in their history.
Rudi Garcia's side are now two points clear at the top of the table with Napoli second, Juve third, and Inter and Fiorentina - having played a game less than every other team - in fourth and fifth respectively.
Lazio recovered from their Rome derby defeat at the weekend to edge up to sixth thanks to a 3-1 home win over 10-man Catania.
Ederson gave them the a perfect start inside four minutes, only to see Pablo Barrientos equalise shortly before the half-hour mark.
Senad Lulic gave the hosts the advantage once more six minutes before the break and Catania's job was made harder when Giuseppe Bellusci was dismissed for a second bookable offence on the hour. Substitute Hernanes rounded off the scoring in the final minute to condemn Catania to their fourth defeat in five outings this term.
Parma were also involved in a high-scoring affair as they ran out 4-3 winners at home to Atalanta.
Djamel Mesbah put the home side in front after 19 minutes, only for Giacomo Bonaventura to level matters a minute later.
Marco Parolo on 28 minutes and Aleandro Rosi on 35 then gave Parma a two-goal lead before Parolo bagged his second five minutes before half time to put the home side in total control.
German Denis pulled a goal back a minute before the break and Atalanta were given further hope when Amauri was dismissed on 52 minutes for a professional foul. Marko Livaja's strike 11 minutes from time set up a nervy finish, but Parma held on to condemn Atalanta to their third successive defeat.
Torino moved up to eighth after a 2-2 home draw with Hellas Verona, with Alessio Cerci putting the hosts ahead from the penalty spot nine minutes before the break, though Juanito sent the sides in level with a goal in the 44th minute.
Cerci doubled his tally on 52 minutes but Jorginho's penalty 15 minutes later ensured the points were shared.
Meanwhile, Cagliari's winless streak was extended to four games with a 1-1 draw at seventh-placed Livorno.
Andrea Luci put Livorno ahead midway through the first half before Victor Ibarbo's equaliser in the 53rd minute secured Cagliari's third successive draw.