)
Italy attacker Insigne's 31st-minute penalty secured a big three points for Gattuso, whose job is widely reported to be under threat after a poor recent run of results.
The 29-year-old bagged the winner after Giorgio Chiellini had been caught by VAR officials striking Amir Rrahmani with his hand while challenging for the ball.
The win puts Napoli in fourth, level on 40 points with Roma and Lazio and two behind Andrea Pirlo's third-placed Juve, who had been in good form in recent weeks but could end the day 10 points behind league leaders AC Milan.
Seven-time European champions Milan, chasing a first league title in a decade, face Spezia in Saturday's late match looking to extend their lead on second-placed Inter Milan to five points.
)
)
)
Milan hope to take advantage of their two main title rivals having tough opposition this weekend, with Inter hosting a Lazio side on a run of six straight league wins on Sunday night.
Earlier Torino were held to a forgettable goalless home draw by Genoa which leaves Juve's city rivals just two points above the relegation zone.
Torino have now drawn half of their 22 matches but have only won twice all season.
td/mw