The match against Juventus ended 0-0 on the night in Rome, thanks largely to Gigi Buffon heroics and the woodwork, but the Partenopei won on penalties for their sixth Coppa trophy.
“We gave our all because we want to achieve something truly special," Mertens told RAI Sport.
“We all stayed behind in Naples during the lockdown, the staff did great work with us and we were ready to go. When you play in Naples, it's truly special and the fans are wonderful, but we won as a team tonight and the victory started during the quarantine."
On his contract, Mertens added: “I thought long and hard, but this squad, the coach, his staff – as let's not forget it's not just Gattuso – are spectacular for those who play here. Then there's the city…
“For me, a lockdown was like a vacation, I was so happy just being in Naples. That's when I decided to sign the contract."