Inter Milan went on a rare scoring spree to thrash Serie A newcomers Frosinone 4-0 and go clear at the top on Sunday, the first time Roberto Mancini's team have won a league match by more than one goal this season.
Fiorentina, previously level with Inter, needed two goals from substitute Nikola Kalinic to rescue a 2-2 draw at home to lowly Empoli after they had trailed 2-0, with coach Paulo Sousa admitting he had made mistakes with his team selection.
Vincenzo Montella made a losing start as coach of Sampdoria, who lost 1-0 at Udinese, and Davide Ballardini, starting a second stint in charge of Palermo, saw the Sicilians held 1-1 at Lazio.
There was an amazing finish at Genoa where Francesco Acerbi scored in the 94th minute for visitors Sassuolo to make it 1-1, only for Leonardo Pavoletti to win it for the hosts almost immediately. Both teams had a player sent off in the first half.
Inter have 30 points from 13 games, two ahead of Fiorentina and Napoli, who ground out a 2-0 win at Verona with second-half goals from Lorenzo Insigne and Gonzalo Higuain.
AS Roma, held 2-2 at Bologna on Saturday, are a further point behind in fourth.
Jonathan Biabiany pounced on a rebound to put Inter ahead in the 29th minute and Mauro Icardi doubled their lead early in the second half from Adem Ljajic's pass.
Inter, who had scored only 12 goals in their first 12 games and won eight times by single-goal margins, added late goals through defender Jeison Murillo and substitute Marcelo Brozovic.
Fiorentina's Sousa conceded he picked the wrong team after watching Marko Livaja and Marcel Buechel give Empoli a 2-0 halftime lead.
"Before the game, I was convinced that this was the best lineup. But, reviewing the first half, I would not field it again, of course not," said the Portuguese coach.
The visitors could easily have gone three ahead as Saponara fired over and then had a strong penalty appeal waved away.
The game changed dramatically in the second half after Fiorentina brought on Croatia forward Kalinic who reduced the arrears with a header in the 56th minute and turned in Khouma Babacar's pass to level just after the hour.
In a dramatic finale, Kalinic hit the bar and saw another effort blocked by Lukasz Skorupski who also made a superb save in stoppage time to turn away Matias Vecino's long-range shot.
Emmanuel Badu's first-half goal for Udinese ensured a losing start for new Sampdoria coach Montella, whose predecessor Walter Zenga was fired after only 14 matches. The visitors also had Ervin Zukanovic given a straight red card.
Ballardini made his Palermo debut against Lazio, where he spent an unhappy six months in 2009-10, and saw defender Edoardo Goldaniga give the Sicilians a first-half lead before Antonio Candreva levelled with a second-half penalty for Lazio.
Tempers flared just before halftime in Genoa when Sassuolo's temperamental striker Domenico Berardi was sent off for a wild kick at Cristian Anseldi and Diego Perotti was dismissed for the hosts as he also got involved.
Venezuela midfielder Tomas Rincon put Genoa ahead with a curling effort early in the second half before an astonishing finale.
Acerbi levelled with a rebound four minutes into stoppage time but Sassuolo had barely finished celebrating when Pavoletti headed in Genoa's winner.
Two early goals from Roberto Inglese and Riccardo Meggiorini gave Chievo a 2-1 win at Carpi and Torino won 1-0 at Atalanta thanks to Cesare Bovo's volley in the afternoon's other games.