Rafael Benitez failed to deliver Champions League football to Napoli as his final act before leaving the Serie A club for pastures new ended in a 4-2 defeat at home to Lazio.
Lazio were three points clear in third place heading into Sunday night's end-of-the-season encounter in Naples but the hosts' superior head-to-head record meant a win would see the teams swap places.
While Marco Parolo and Antonio Candreva asserted Lazio's authority with first-half goals, Benitez was eager to sign off in style before completing his reported move to Spanish giants Real Madrid.
During half-time he motivated his players to hit back and Gonzalo Higuain's quickfire brace rocked the Biancocelesti before the Argentinian missed a penalty to cool Napoli's comeback.
Substitutes Ogenyi Onazi and Miroslav Klose then rubber-stamped Lazio's victory and with it a third-placed finish.
The remit was clear at a bouncing Stadio San Paolo - Napoli needed to beat their visitors from the capital city to snatch the last Champions League place.
But, despite the efforts of a partisan crowd, they struggled to get going and it was not until the 12th minute that they carved out a chance that saw Higuain pass the ball into Federico Marchetti's legs.
Gokhan Inler could not make any of his passes stick and when Jose Callejon darted into the area to connect with one of the better efforts, Marchetti was on hand to smother.
Lazio capitalised on their hosts' uncertainty and opened the scoring against the run of play in the 33rd minute.
It was a fine goal that brought Parolo into double figures for the season, the former Parma midfielder cutting inside from the left before driving the ball over Mariano Andujar's shoulders and home.
Napoli looked shell-shocked and failed to respond with half-time rapidly approaching, and they were duly punished.
One minute into stoppage time Lazio doubled their lead and tightened their grip on third place as Senad Lulic sent Candreva into a one-on-one with Andujar that the Italy midfielder won with ease.
Another Napoli side might have crumbled but Benitez's team returned to the field determined to overhaul the two-goal deficit and force their way into Europe's top competition.
Higuain made it 2-1 when clipping home Jose Callejon's pass across the goal-line, and the Azzurri would have been level on 57 minutes had Stefan de Vrij not cleared Dries Mertens' shot off the line.
Parolo's dismissal for earning a second yellow card allowed Napoli the space they needed to supply Higuain in the 64th minute.
The Argentinian timed his run perfectly and took Mertens' assist in his stride before beating Marchetti to inspire raucous cheers of fresh belief at the San Paolo.
Faouzi Ghoulam became the second player to be sent off when he went in late on Cristian Ledesma to pick up a second booking, evening up the teams ahead of what would be a frantic finale.
It seemed like fate when Napoli were awarded a penalty in the 76th minute.
On a hat-trick, Higuain stepped up to the spot after Lulic impeded Christian Maggio, but his attempt to convert the treble ended up in the crowd.
Victory remained within the Neapolitans' reach until the 85th minute, when Lazio substitute Onazi decided otherwise.
The Biancocelesti were finally assured of a crack at the Champions League play-offs when the Nigerian striker beat Andujar with a cool finish only two minutes after entering the fray.
Napoli's race was run and Benitez's two-year reign was finally over when veteran striker Klose provided the luxury of a fourth goal when emerging from the bench to turn home Ledesma's free-kick.
ends