The game, which began with Napoli two points ahead of Juve, appeared to be petering out into a goalless draw when the shaven-headed Zaza collected the ball with his back to goal, turned and fired an unstoppable left-foot shot past Pepe Reina.

Zaza has struggled for a place in the team this season, was the subject of media speculation over a move in the transfer window and appeared to have blown his chance altogether when he was sent off against Genoa in his last appearance.

"It was a very tactical match and this was an important moment in the championship on a psychological level," said Juve coach Massimiliano Allegri.

Juve defender Leonardo Bonucci was also at the heart of the action after he collided with team mate Sami Khedira early on, made a crucial interception to prevent an almost certain Napoli goal and went off injured after halftime.

Napoli, aiming to win the title for the first time since 1990, had won their previous eight games and boasted the league's most prolific attack with 53 goals.

However, experienced goalkeeper Gianluigi Buffon barely had a save to make as Juve's defence, the stingiest in the championship, prevailed.

Juve, who were 11 points adrift of first place after 10 games this season, now lead with 57 points, one ahead of Napoli, and look favourites to clinch a fifth successive title.

AS Roma, who are 10 points off the pace in third spot, won 3-1 at Carpi on Friday.

TIGHT GAME

Napoli coach Maurizio Sarri was left to rue a momentary lapse of concentration by his team.

"It was a tight game with few chances. We gave almost nothing away and only lost because of one unfortunate episode," he said.

Juan Cuadrado tested Napoli keeper Reina after 13 minutes with a long-range shot before team mate Paul Pogba curled a free kick narrowly wide from about 30 metres.

A Napoli goal looked on the cards when Elseid Hysaj's cross looked to be heading straight to Gonzalo Higuain, unmarked in front of goal, but Bonucci came from nowhere to stick out his leg and deflect the ball for a corner.

Bonucci, still struggling from his early clash with Khedira, eventually went off early in the second half. Even after he was replaced by the less experienced Daniele Rugani, Juve held firm.

A moment of brilliance from Pogba nearly unlocked the Napoli defence on the hour as the Frenchman controlled the ball on his chest and slipped it inside to Paulo Dybala whose shot flashed over the crossbar.

An anti-climatic stalemate seemed likely until Zaza produced his moment of inspiration to send the Juventus Stadium wild.

"I stopped him from leaving in January as I did with other players," said Allegri. "Between now and the end of the season the difference will be made by the players who have played less and are freshest in the mind."