Carlo Ancelotti’s Napoli have 12 points from five games, equal with champions Juventus who can pull ahead again when they travel to promoted Frosinone later on Sunday.
But Roma coach Eusebio Di Francesco is under increasing pressure after a fourth league game without a win sees last year’s third-placed team slump to 12th with five points from as many games.
Federico Mattiello and Federico Santander scored in either half to give Bologna, who occupy the first relegation spot of 18th position, their first goals and win of the season.
“I’m not the type to look for excuses, I need solutions and I can not find them,” said Di Francesco.
“The facts condemn us, they condemn me.”
In Turin, Ancelotti switched things around following Napoli’s uninspiring goalless draw at Red Star Belgrade in the Champions League midweek.
Insigne played a more central role along with Dries Mertens as defender Sebastiano Luperto got his first start for the Serie A runners-up.
“I’m satisfied, we dominated in Belgrade but we couldn’t finish things off like we did today,” said Ancelotti.
“Insigne was decisive, but everyone put in a strong performance.”
The Italian international got the first after just four minutes when poor Torino defending saw Emiliano Moretti clear to Nicolas N’Koulou with the rebound favouring Insigne, who finished off under the crossbar.
Simone Verdi added the second with a half-volley on 20 minutes, with Torino pulling one back after the break when Andrea Belotti slotted in a penalty.
But Insigne restored Napoli’s two-goal lead after 59 minutes when a Jose Callejon shot bounced off the inside of the far post and into the path of the Italian forward.
It gives Napoli a boost ahead of next week’s trip to reigning seven-time champions Juventus.
“We won there last season and still finished second,” said Insigne.
“If we don’t win the midweek game with Parma, then the result with Juve is irrelevant, so we have to take it one at a time.”
Torino are in 13th position with five points from as many games.
‘No inner fire’
In Bologna, Roma plunged further into crisis after a summer which saw Di Francesco’s side lose goalkeeper Alisson to Liverpool with midfielders Radja Nainggolan and Kevin Strootman also exiting the Italian capital.
Mattiello curled in Bologna’s first goal of the season after 36 minutes with Paraguayan Santander adding the second after 59 minutes.
Roma — last year’s Champions League semi-finalists — also fell 3-0 at Real Madrid midweek, and have not won a league game since their first game against Torino.
“There’s no inner fire,” lamented the Roma coach. “Something is wrong.”
Next weekend Roma face bitter city rivals Lazio, who saw off Genoa 4-1 on Sunday with Ciro Immobile scoring a double, to move up to fifth place.
Before the derby Roma will try to boost morale against Frosinone midweek with Lazio heading to Udinese, who won 2-0 at Chievo.
Inter Milan snatched a late 1-0 win against Sampdoria in Genoa on Saturday to move up to ninth.