"It's an own goal that hurts me because it came after an incredible comeback," Koulibaly later said on Twitter. PHOTO: AFP
The Senegal international shanked in Paulo Dybala's free-kick under no pressure in the second minute of stoppage time to hand Juve the three points in Turin and put Maurizio Sarri's side top with a maximum six points, leaving Napoli with nothing to show for their Herculean efforts.
"It's an own goal that hurts me because it came after an incredible comeback," Koulibaly later said on Twitter.
"I'm sorry but I have to -- we have to accept it: we are strong. We have shown that. We're going to prove it."
Koulibaly's blunder undid all of Napoli's good work in fighting back from the dead with less than half-an-hour left, with goals from Danilo just 20 seconds after he came on as a substitute, Gonzalo Higuain -- back at Juventus after loan spells at AC Milan and Chelsea -- and Cristiano Ronaldo on 61 minutes giving the reigning champions what looked like an unassailable lead.
However two goals in as many minutes from Kostas Manolas and Hirving Lozano shortly after Ronaldo had made it three brought Napoli back into the game, and Giovanni Di Lorenzo sent the away fans wild with a close-range finish to set up a tense final nine minutes.
But with at least point seemingly in the bag, Koulibaly made it a nightmare end for Carlo Ancelotti's men, who finished on the wrong end of a 4-3 scoreline after winning by the same margin at Fiorentina last weekend.
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"It was a rollercoaster. We lost control of the game and got distracted, so they managed to equalise, but fortunately in the end we still won," said Higuain, who spun Koulibaly before slamming home Juve's superb second.
The champions made light of the absence of captain Giorgio Chiellini, out with anterior cruciate ligament knee injury, and Sarri, who is battling pneumonia and was not on the bench.
Ancelotti meanwhile was left to regret a "wasted opportunity" after losing in such gut-wrenching fashion.
"It was not a positive performance. The first hour we didn't do well. But despite the 3-0 we stayed in the game, we came back," said Ancelotti.
"Juventus have so much character and quality, we know that they always step up in the important moments of the season.
"We wasted an opportunity today."
Earlier Turkey midfielder Hakan Calhanoglu claimed AC Milan's first three points of the season after scoring the only goal in a 1-0 win over newly-promoted Brescia.
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The 25-year-old connected with a cross from Spanish winger Suso to head a 12th-minute winner after Milan had lost their opener to Udinese last weekend.
Poland forward Krzysztof Piatek, who finished third in Serie A's scorers chart last season with 22 goals, Lucas Paqueta and Fabio Borini all started on the bench for the side who have been banned from this season's Europa League for breaking financial fair play rules.
Dimitri Bisoli missed a chance to equalise, sending a shot over the bar with Milan goalkeeper Gianluigi Donnarumma denying Ricardo Rodriguez's deflected shot before the break.
Piatek come on for the last half an hour in place of Andre Silva, with Paqueta replacing Calhanoglu five minutes later.
The hosts came to life in the final 10 minutes with Piatek missing a chance to get a second goal for Milan, then setting up Paqueta who also drew a blank.
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