Speaking to Mediaset Premium, the hero of Napoli's first victory at Allianz Stadium was adamant they have always backed themselves to keep the pressure on Massimiliano Allegri's men.
Juventus are bidding for their seventh Serie A title in succession and 34th in total, whereas Napoli have only been champions twice in their history - in 1987 and 1990.
Allegri, meanwhile, defended his side who showed signs of tiredness after a gruelling season in which they were eliminated from the Champions League by Real Madrid in the quarter-finals.
The closest Juve came to a goal was in the first half when Miralem Pjanic hit the woodwork with a deflected free-kick.
The legendary Italian stopper went in among the Napoli squad as they celebrated their victory wildly and congratulated every single player. We had some difficulties, but we should've taken it to the end more carefully rather than concede a goal from a set play.
"The team believes, yesterday we saw the image of a team that doesn't give up, which is focused and which has the right adrenaline to overcome the obvious physical problems of recent matches". When you play at the rate we do, I think it's normal to be exhausted.
"We knew it was a very hard and important match, but we did everything to win, we did it and can be proud of ourselves", said 26-year-old Koulibaly.
Lazio and Inter Milan kept their push for Champions League football alive on Sunday.
"Now, for us, Saturday's match against Inter is the really decisive one".
Lazio dominated Sampdoria in their Stadio Olimpico with Sergej Milinkovic-Savic breaking through after 32 minutes and a Stefan de Vrij diving header giving the hosts a second just before the break.
The battle for Europe could go down to the wire with Lazio hosting Inter in their final game of the season.