What a night! Plenty of talk before the game was about the possibility of another European classic at the Bridge and that is exactly what those watching enjoyed.
It needed extra time and a Branislav Ivanovic goal to win it but the Blues showed bags of character to turn this tie around.
But then Napoli, who played their part in the occasion with a very watchable style of football, netted to take them back in front on aggregate, only for Frank Lampard to make the tie absolutely level from the penalty spot.
Goals looked possible at either end as the minutes ticked on but happily, it was the Blues who did the business to make the quarter-finals and maintain an English challenge in the competition.
David Luiz returned to central defence with Gary Cahill making way. In midfield Michael Essien replaced John Mikel Obi and Frank Lampard dropped back from his advanced role against Stoke, with Raul Meireles suspended. Daniel Sturridge took the place of Salomon Kalou but played on the right flank with Ramires unusually on the left.
Napoli were unchanged from the first leg.
Although Chelsea dominated possession at the very start, the game soon settled into the predicted pattern - the home team probing away in front of a well-manned opposition defence but then stretched from time to time by the rapid Napoli attacking play.
Lampard challenged Edinson Cavani hard in the opening seconds but conceded a free-kick on that occasion and Terry sent a header well off-target from a Chelsea free-kick, taken by Mata. The first proper effort was by Sturridge, a shot along the deck that the keeper scrambled past the post.
On nine minutes Napoli for the first time caused trouble for Chelsea, a Hamsik shot deflecting off Terry and needing Cech to quickly shift his weight and save with his legs. Three minutes later the Neapolitan side unleashed just the type of counter-attack that had hurt Chelsea in the first game - Maggio charging into space on the right and firing low to the far post where on this occasion, Cavani shot wide.
It was worrying times for the Blues and Cech was soon asked to save again, this time from Ezquiel Lavezzi after a very good pass had beaten the offside call.
The coveted early goal for Chelsea hadn't come. Midway through the half Ramires did well to take a Mata pass and spin into the area but the reputedly suspect Napoli rearguard was defending well.
It was hard to spot where a Chelsea breakthrough could come from but then Ramires was given the ball out by the left touchline and worked it onto his right foot for a cross. It was perfect for Drogba to head down into the bottom of the Shed End net. We were ahead on the night with 27 minutes played.
We could have been ahead in the tie just a minute later had Hugo Campagnaro not reached the ball just in front of Drogba who looked certain to tap in a Sturridge cross.
The Napoli threat remained and Cavani dragged a shot wide after Inler had sent him clear to the frustration of the Napoli fans, but then Sturridge headed not too far wide at the other end.
There was a forced change for the Italian side 10 minutes before the break. Right wing-back Christian Maggio, so lively in the first leg, had not recovered from an early challenge from Ramires whose selection on that wing might have been to use his running against the Italian international. Maggio was replaced by former Liverpool man Andres Dossena.
Lampard was the first player cautioned, for a 42nd minute foul on Zuniga. It was a stop-start, whistled-filled end to the opening period. In stoppage time David Luiz hammered the ball into the six-yard box and Cannavaro stretched to cut it out, very much running the risk of an own goal in the process.
The half was barely a minute old when Cannavaro carelessly headed over his own goal to give Chelsea a corner to cue up a time-honoured combination. Lampard placed his set-piece delivery towards the near-post area where Terry was running towards and the skipper flicked the perfect header over De Sanctis and in.
Napoli had conceded a third of the goals against them this season from headers and it was proving their Achilles heel tonight. Now they had to score.
Cannavaro was booked for a foul on Lampard but the Napoli response was good as Chelsea were soon asked to do plenty of work back in our own area. We conceded an away goal on 54 minutes when Terry initially headed clear a cross but Inler controlled the ball on his chest and sweetly struck it into Cech's net from the edge of the area. Now Chelsea needed a goal.
Just prior to Napoli scoring, Di Matteo had been about to bring on Jose Bosingwa, possibly to play on the wing rather than at full-back, but that moment had passed. Instead Torres entered the action with just over an hour played.
The Spaniard was soon foraging hard inside the Napoli area and the ball broke to Ivanovic who smashed a shot that the keeper hurriedly blocked. Then after another Chelsea corner, Drogba battled, spun and unleashed a volley that needed the save of the game from De Sanctis to keep it out of the net.
Dossena was booked on 67 minutes for catching Essien on the thigh before Zuniga came off the flank to force another save from Cech. Some of the Chelsea defending was by now falling into the last-ditch category.
At the other end the corners kept coming, each one bringing hope, and there was a scramble after a sliced Napoli clearance when Drogba had headed on.
The Blues kept the pressure on and Napoli cracked, Dossena clearly handling an Ivanovic header and on this occasion it was spotted by a Champions League ref - Felix Brych from Germany pointing to the spot.
Lampard smashed the penalty in to make the scores level on aggregate with 74 minutes played.
The challenges from both sides strengthened. It was a night of blood and thunder, thrills and spills. The Stamford Bridge crowd responded.
With 86 minutes played, David Luiz did well to juggle the ball away from a lurking Cavani and moments later Walter Gargano launched an ambitious effort onto the roof of the Chelsea net. Before the 90 minutes were up, Drogba was wanting a penalty after he and Aronica tangled but this time the ref wasn't interested. Another 30 minutes was to be played.
Extra time first half
The Chelsea threat in the air continued on unchecked - Ivanovic this time heading a corner a yard wide, but then Napoli counter-punched with a fierce Hamsik volley that went equally close.
Malouda was the second Chelsea substitute introduced, replacing Mata four minutes into extra time with Bosingwa on three minutes later, a forced change due to a Terry injury. Rather than bring Cahill on, Ivanovic moved into central defence. Moments before that switch, Cole had been shown a yellow card for fouling Campagnaro.
De Sanctis in the Napoli goal had done well on the night but completely misjudged a long punt forward by Drogba, running underneath it to allow Torres in behind him, but the angle was always against the Spaniard finding the target.
A minute before the interval Chelsea did go ahead - Drogba the craftsman and Ivanovic applying the gleaming finish. In a tight space, the Ivorian wriggled clear enough to cross low and the Serbian turned it in first time from 12 yards out.
Extra time second half
Ahead on aggregate, now Chelsea could play on the counter-attack and Torres made De Sanctis sprawl to save his long-range shot after Ramires had broken forward.
It was desperate times for the Italian side and Inler and Campagnaro were both booked. One goal for them would turn the tie from a Chelsea win to a Napoli one however, and football doesn't get any more tense than that.
We could have made it safe with less than a minute left on the clock after Malouda nicked possession high up the pitch and fed Drogba but he volleyed wide. But the four goals proved to be enough. It was time for 'One Step Beyond' as Chelsea took another step forward.
We will discover our next opponents when the draw is made on Friday.
Chelsea (4-4-1-1): Cech; Ivanovic, D Luiz, Terry (c) (Bosingwa 97), Cole; Sturridge (Torres 62); Essien, Lampard, Ramires; Mata (Malouda 94); Drogba.
Unused subs Turnbull, Cahill, Mikel, Kalou.
Scorers Drogba 28, Terry 47, Lampard pen 75, Ivanovic 104.
Booked Lampard 42, Cole 97.
Napoli (3-4-2-1): De Sanctis; Campagnaro, Cannavaro (c), Aronica (Vargas 109); Maggio (Dossena 36), Inler, Gargano, Zuniga; Hamsík (Pandev 106), Lavezzi; Cavani
Unused subs Rosati, Dzemaili, Fernandez, Britos.
Scorer Inler 54
Booked Cannavaro 52, Dossena 67, Inler 111, Campagnaro 114.
Referee Felix Brych from Germany.