Walter Mazzarri's men gave away the lead on two occasions and then imploded in the closing stages of normal time, enabling the Turin side to secure their fifth Supercoppa title
Edinson Cavani handed the side from Naples the lead after 27 minutes but his strike was cancelled out by Kwadwo Asamoah 10 minutes later. Goran Pandev pounced on a defensive error to regain Napoli's advantage before half time but a penalty from Arturo Vidal tied the score at 2-2 in the 76th minute.
The Azzurri self-destructed towards the end of normal time as Pandev, their coach Walter Mazzarri, and Camilo Zuniga were all sent from the field of play. Juve then took full advantage of their additional men in the extra time that followed as a Cristian Maggio own goal was followed by a winner from Mirko Vucinic.
Due to Antonio Conte's 10-month suspension banning him from the touchline, his assistant Massimo Carrera took charge of the Bianconeri for the game. They assumed control inside the opening 15 minutes but for all of Stephan Lichtsteiner's continual forays down the right flank, the creation of a clear-cut opportunity remained elusive.
Juve's inability to test Morgan De Sanctis ended up costing them dearly in the 27th minute when a high defensive line allowed Cavani to stream through on goal. He attempted to round Buffon and although the keeper got a hand to the ball and forced him wide, the Uruguayan remained composed and stabbed his effort home.
Napoli failed to capitalise on a poor throw-in from Asamoah as Buffon held Pandev's volley from inside the area but the Ghanaian more than atoned for that lapse in the 37th minute. A long ball from left to right by Vidal was lashed into the bottom corner with a perfectly executed 18-yard volley from Asamoah.
However, the scores were not tied for long as the Azzurri regained their advantage four minutes before the break. Leonardo Bonucci's clearance rebounded off of Pandev's chest and put him in on goal from the left wing. The defender's efforts to chase him down were in vain as the forward produced a delicate finish, dinking the ball over Buffon and into the net.
Vucinic replaced Alessandro Matri for the Turin outfit at half time and his introduction certainly galvanised his side. After three minutes he rattled the bar and he then saw his goal-bound effort, after rounding De Sanctis, blocked by Paolo Cannavaro before the hour mark.
Andrea Pirlo had a long-range free kick saved between the Montengrin's two efforts but the Bianconeri's improved attacking display eventually paid dividends with 16 minutes left on the clock. Vucinic was dragged down in the area by substitute Federico Fernandez and Vidal converted the penalty, sending the keeper the wrong way.
The game became increasingly ill-tempered and Pandev and Zuniga were shown utterly stupid red cards, the former for dissent and the latter for two clumsy challenges, in the closing stages, while coach Mazzarri was also sent from the touchline. With the score level at the final whistle the game went to extra time and Napoli were thus forced to contest it with nine men.
The reigning Serie A champions made their two-man advantage count with a pair of goals in the first half of the additional 30 minutes. Maggio diverted a Juve free kick from the right into his own goal after De Sanctis failed to clear and Vucinic added the finishing touch to a delightful flick from Claudio Marchisio to put the game well beyond the Partenopei.
The final whistle was greeted by scenes of jubilation among the Bianconeri players who lifted the fifth Supercoppa Italiana in the club's history in what was a game that truly had everything and served as a fantastic curtain-raiser for the 2012-13 domestic Italian season which begins in two weeks.