Siena, who began with a six-point deduction for their part in the Calcioscommesse match-fixing scandal, moved up to minus one points after their first win of the season.
Inter, who have six points after winning their two away games, dominated the game only to be beaten by two late counter-attacks.
City rivals AC Milan's season slumped to a new low too as they had two players sent off and lost 2-1 at Udinese while the bizarre postponement of the Cagliari-AS Roma match further damaged Serie A's fading credibility.
Roberto Di Natale scored the winner for Udinese with a 68th minute penalty, while the visitors had Cristian Zapata and second-half substitute Kevin-Prince Boateng dismissed in their third defeat in four Serie A games.
Neither Milan nor Inter have won a game at San Siro this season in any competition in eight attempts between them.
Napoli, Sampdoria and Lazio all lost their 100 percent records, leaving Juventus as isolated leaders with 12 points from four games after their 2-0 win over Chievo on Saturday.
Napoli, who have 10 points, were held 0-0 at Catania and Sampdoria were held 1-1 at home by Torino in a match between two promoted teams.
Sampdoria have nine points, having had one deducted over their involvement in the Calcioscommesse match-fixing scandal.
Lazio slumped to a shock defeat 1-0 defeat at home to Genoa as they dominated the game, missed a hatful of chances and were caught by a breakaway goal scored by Marco Boriello in the 79th minute.
Palermo's latest coach Gian Piero Gasperini got off to a losing start as his side lost 1-0 at Atalanta and promoted Pescara picked up their first point with a 1-1 draw at Bologna.
Gasperini's hopes of lasting longer than his predecessors at Palermo were dented when Cristian Raimondi's 88th minute goal sent them to a 1-0 defeat at Atalanta, leaving the Sicilians with one point.
Gasperini replaced Giuseppe Sannino, fired after only three games by Palermo's volatile president Maurizio Zamparini, who has employed an average of two coaches a season at the club over the last decade.