Three years ago Barcelona thrashed Napoli 5-0 in a friendly but at the Stade de Geneve on Wednesday, Rafael Benitez's Italian side triumphed thanks to Dzemaili's 80th-minute strike.
Barcelona goalkeeper Claudio Bravo shanked a clearance after pressure from Michu and Dzemaili collected the loose ball.
The Swiss midfielder's looping shot from 25 yards then slipped through Bravo's hands to complete a terrible minute for the Chilean goalkeeper and give Napoli victory.
"I'm really happy for this goal, I tried and I know the potential of my shot," Dzemaili told Napoli's website after the match.
"I struck the ball in the right way and hit the target."
The win will give Napoli fans hope Benitez's team can improve on their third-placed finish in Serie A last season and their group stage exit in the UEFA Champions League.
"We are certainly more mature and furthermore many talented players joined us and we have a longer experience," Dzemaili said.
"Now we should pursue this track and grow more and more."
Dzemaili is about to start his fourth season with Napoli but the 28-year-old has yet to secure a regular starting berth in his previous three campaigns.
Last season, Dzemaili made 24 appearances in the Serie A, starting 18 times.
He has played a total of 86 Serie A matches for Napoli, including 58 starts.
The Macedonia-born Switzerland international was also used off the bench at the World Cup but did not seem too frustrated with the prospect of limited game time this season, underlining the importance of a strong squad as Napoli look to improve.
"Everytime the coach lets me play I'm ready, I do my best on the pitch to open up space," he said.
"We are a strong group and all of us should be eager to play when we have the chance."
