Vincent Aboubakar scored twice, including a late winner, as Beşiktaş finally saw off Napoli for a crucial Group B victory having twice let the lead slip.
Beşiktaş opened the scoring on 12 minutes, as Adriano capped a beautiful team effort. Tolgay Arslan's no-look pass found Ricardo Quaresma on the right and the Portuguese winger set up Adriano for a tap-in.
The hosts responded on 30 minutes, Dries Mertens finishing a similarly slick move involving Marek Hamšík and Jose Callejón. Aboubakar, however, restored the away team's advantage before half-time, rounding off a great counterattack.
Napoli wasted a great chance to lead when goalkeeper Fabri blocked Lorenzo Insigne's penalty five minutes into the second period, although when they were awarded another spot kick 19 minutes later Manolo Gabbiadini made no mistake.
Just as the game seemed destined for a draw, Aboubakar rose highest to meet a Quaresma free-kick and give Beşiktaş three points.
Key player: Vincent Aboubakar (Beşiktaş)
Until now, the Cameroon striker had had a rough start to life at Beşiktaş, playing seven competitive matches without scoring. What a way to open his account! He was mobile, clinical and made his presence felt throughout, no more so than with his two deserved goals.
Güneş's Italian jobs
Şenol Güneş's UEFA Champions League career is full of draws (six in eight games before tonight) – and now two famous victories in Italy. The Beşiktaş coach has managed to get the better of Napoli, five years after shocking Internazionale with Trabzonspor. Beşiktaş were well-disciplined, patient and clinical when given the opportunity.
Adriano after giving Beşiktaş the lead in Naples
Missing Milik leaves Napoli short
Nine or false nine? This will be the question for a few months as Napoli boss Maurizio Sarri searches for a solution to Arkadiusz Milik's injury absence in attack. Mertens did well as a false nine in the first half and scored, yet he also wasted a couple of good chances and looked more comfortable in his usual role on the left when Gabbiadini came on. Gabbiadini himself converted a penalty and had a wonderful overhead kick ruled out for offside. Probably too close to call, but Napoli seemed better with a out-and-out striker today.
Paolo Menicucci, Napoli (@UEFAcomPaoloM)
When you miss lots of opportunities and make several mistakes in defence, you should not be surprised if you lose. This is exactly what happened to Napoli against a lethal Beşiktaş, who gave the Partenopei a lesson in efficiency. Napoli still top Group B but having had the chance to become the first team to qualify after only three matches, they now find themselves in a tricky situation with difficult away games against Beşiktaş and Benfica in their last three fixtures.
Çetin Cem Yılmaz, Beşiktaş (@UEFAcomCetinCY)
Each of Beşiktaş's UEFA Champions League campaigns have been graced by a famous victory. Barcelona, Liverpool and Manchester United have been beaten, and this Napoli win will go down in club folklore as well. That aside, Beşiktaş are now in a good position to progress, and deservedly so. The Black Eagles played a well-disciplined game, stopped Napoli's high-pressure approach early on, and were rewarded by their clinical finishing.