The midfielder scored the final goal in the Serie A side's 3-1 home win over Swansea City on Thursday, which secured their place in the last 16 of Europe's secondary club competition after a goalless first leg in Wales.
Lorenzo Insigne opened the scoring early for Napoli, but Jonathan de Guzman's equaliser on the half-hour mark had Swansea on course to progress on away goals.
However, Gonzalo Higuain struck for the hosts 12 minutes from time before Inler sealed a tie with Porto in injury time.
And Inler believes Rafael Benitez's men will need to improve in order to defeat the Portuguese champions.
"We suffered a lot, but this is also a beautiful and well-deserved victory," the Switzerland international told the club's official website.
"Having scored the first goal we did not relax because we knew that it was an open game and in fact they scored a goal that slowed us down.
"Certainly we need to improve in some stages of the game, but in the end we did well to push and find this important success.
"Now let's look forward in the league and the next round.
"We have dealt with Porto in a friendly last summer but it will certainly be different story now. We are equipped with a team of great players."
Insigne, meanwhile, was quick to praise the team spirit within Napoli's squad, but also paid tribute to Swansea for contributing to close encounter.
"I'm happy for the goal, but it was the success of the team (that was important)," he said. "We were all united to the end and we were able to win this game.
"We know any team in Europe can make you suffer, but we fought to the end and our efforts have paid off."
