Arriving at Stamford Bridge with a 3-1 advantage from the first leg, Napoli played their full part in a thrilling game in west London before losing 4-1 after extra time - Branislav Ivanovic's goal earning Chelsea a 5-4 aggregate victory.
Had Edinson Cavani, Ezequiel Lavezzi or Marek Hamsik taken any of the numerous chances Napoli carved out in the opening 25 minutes, the talk on Thursday would not have been of Chelsea's old guard but of a new force in Italian football.
Napoli never capitulated and but for a rather needless handball by substitute Andrea Dossena in the 75th minute, which offered Frank Lampard the chance to take the tie to extra time, they would be in Friday's draw for the last eight.
They must now dust themselves down and concentrate on a top-three finish in Serie A to ensure another crack at Europe's showpiece club tournament.
Currently they are fourth, two points behind Lazio with 11 matches remaining. Only the top two in Italy qualify automatically with the next best team facing a playoff.
"We made too many mistakes and we should have been more careful, but I am proud of my players," Mazzarri told reporters. "We learned a lesson that we need to take for going forwards.
"We now have 11 finals until the end of the season, we need to try and go for it and try and finish higher than third place and go for the Champions League again.
"Now we have important games against Udinese and Siena and we must try and reverse this result and whatever the final results are of this season.
"I think we can be proud of what we have done. In terms of how we can recover from tonight - I know the team, I know this group of players and we can learn from the mistakes we made."
The fact that Chelsea's players celebrated so wildly at the end was a back-handed compliment to Napoli.
The likes of Frank Lampard and John Terry, veterans of three Premier League title campaigns and many great European nights, said beating Napoli had topped the lot.
"This goes in at Number One," said Lampard. "Because we came back from 3-1 down against a very good side who played extremely well on the night."
The worry for Napoli now will be keeping hold of the likes of Cavani, Hamsik and the impressive Christian Maggio, all of whom are on the radar of Europe's biggest clubs.
"We have a young team so we can learn from this experience," said Mazzarri. "We are disappointed that we have not brought more joy to our fans. In some parts of the game I think we played better than Chelsea, we showed some quality."
They may be out but Napoli's debut in the tournament was a great advert for Serie A and their brand of attacking football would be welcomed back next season.