Previous leaders Napoli slumped to third in Serie A on Sunday as they succumbed to a surprise 3-2 defeat at the hands of lowly Bologna.
Napoli had gone top of the table on Monday after they beat 10-man Inter in Naples but Roberto Mancini's men recovered on Saturday with a 1-0 win over Genoa.
Victory would have taken Napoli back to the summit but a sluggish start ultimately cost Maurizio Sarri's side as Mattia Destro and Luca Rossettini put the hosts' two goals ahead after just 21 minutes.
Destro scored again on the hour, with Gonzalo Higuain's brace failing to inspire a comeback as Napoli lost for the first time since their opening-day defeat at Sassuolo.
Fiorentina's 3-0 win over Udinese made matters worse for Napoli - Paulo Sousa's men moving a point behind Inter in second thanks to goals from Milan Badelj, Josip Ilicic and Gonzalo Rodriguez.
Vincenzo Montella's wait for a first win as Sampdoria boss continues, his side going down 3-1 to Sassuolo.
Francesco Acerbi, Sergio Floccari and Lorenzo Pellegrini were on target for the visitors who move above eighth-place Milan into sixth following their goalless draw at Carpi.
Elsewhere, Chievo and Atalanta coped with the dismissals of Simone Pepe and Giulio Migliaccio respectively to see off Frosinone and Palermo.
Late goals from Alberto Paloschi and Riccardo Meggiorini ensured Chievo a 2-0 win at the Stadio Comunale Matusa with German Denis, Nicolo Cherubin and Marten de Roon on target for Atalanta in their 3-0 success.
Veteran striker Luca Toni announced his intention to retire at the end of the season - just short of his 39th birthday - following Hellas Verona's 1-0 defeat to Empoli.
Andrea Costa's goal just after the hour was enough to keep Toni's side bottom of the table, four points adrift of Carpi in 19th and nine off safety.
"I hope to celebrate [retirement] by keeping Verona safe in Serie A," said the former Italy international.
