1013 GMT April 08, 2020
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 its Herculean efforts, AFP reported.
"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 and Cristiano Ronaldo on 61 minutes giving the reigning champion 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 one 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.
"It was a rollercoaster. We lost control of the game and got distracted, so they managed to equalize, but fortunately in the end we still won," said Higuain, who spun Koulibaly before slamming home Juve's superb second.
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 has so much character and quality, we know that they always step up in the important moments of the season.
"We wasted an opportunity today."