Napoli hit the woodwork three times, while Alessandro Diamanti and Matteo Rubin scored in each half for Bologna.
Napoli’s frustration boiled over in the final minute as the two teams became involved in a mass brawl and red cards were shown to Bologna’s Archimede Morleo and Napoli’s Blerim Dzemaili.
Udinese took full advantage, beating nine-man Genoa 2-0 to go third with 61 points, one ahead of SS Lazio, who won 2-0 at Atalanta BC, and three clear of Napoli.
Antonio Di Natale and Antonio Floro Flores scored in each half for Udinese against opponents who had Juraj Kucka and Rodrigo Palacio sent off before halftime.
Fabrizio Miccoli scored a hat-trick as Palermo were held 4-4 at home by Chievo Verona in a match during which both sides squandered two-goal leads, while Parma won 2-0 at AC Siena.
Marco Rigoni scored a hat-trick to give Novara Calcio a 3-0 win over Cesena in a meeting of two teams who have already been relegated.
Additional reporting by staff writer