Napoli's Champions League campaign came to an end after Wednesday's 2-1 loss at Feyenoord as Maurizio Sarri was left to reflect on a damaging start to December.
Having surrendered top spot in Serie A following last week's 1-0 reverse to Juventus, Napoli's European adventure was taken on an unwanted detour to the Europa League, with Shakhtar Donetsk's shock victory over Group F winners Manchester City ensuring the result in Netherlands was inconsequential.
The visitors needed a win at De Kuip and a favour from City, but got neither as the final month of 2017 shaped up to be one to forget for the Stadio San Paolo club.
Deprived of the services of the injured Lorenzo Insigne, Napoli made a superb start and Piotr Zielinski soon broke the deadlock from close range.
Feyenoord, 14 points off top spot in the Eredivisie and aiming to avoid the humiliation of finishing the group phase without a point, looked to be on the ropes as Napoli spurned a number of opportunities, but the hosts found a leveller through Nicolai Jorgensen before the break.
With the odds stacked against them in their bid to qualify, Napoli remained the better side throughout a second half that saw Tonny Vilhena dismissed, but somehow contrived to lose to the 10 men as substitute Jeremiah St Juste headed in the winner at the death.
Napoli, who won the reverse fixture 3-1, were ahead within two minutes as Amadou Diawara's free-kick was headed back across goal and, while Dries Mertens could not turn the loose ball towards the target, Zielinski was on hand to prod home.
Sarri's men should have been two to the good after a neat one-two between Marek Hamsik and Mertens left the latter with only Kenneth Vermeer to beat, but the goalkeeper did well to deny the Belgian.
The chances continued to come for the Italians and Hamsik was denied by Renato Tapia's goalline clearance after bright play from Jose Callejon.
Feyenoord's lack of threat was captured in Steven Berghuis' 20-yard strike, which veered wildly off target before going out for a throw-in.
Word of Shakhtar's opening goal at home to City will have started to filter through by the time Napoli's ambitions suffered another setback.
Berghuis' teasing cross was inch-perfect for Jorgensen, whose header was equally precise, and Giovanni van Bronckhorst's side were still celebrating as Shakhtar doubled their account to render Napoli's hopes increasingly remote.
Although Napoli must have known their fate was practically sealed, they played with a high tempo in the early stages of the second half, forcing Feyenoord onto the back foot.
Marko Rog and then Mario Rui were called upon from the bench in a bid to inject further energy into Napoli, who at the very least seemed determined to sign off with three points.
Pepe Reina took a chance in his own six-yard box when he dummied a clearance before taking the more advisable approach of actually getting the ball to safety, with Jean-Paul Boetius closing in.
Vilhena was given his marching orders when the midfielder received a second yellow card in the 83rd minute following a poorly timed challenge on substitute Adam Ounas.
That should have laid the platform for a Napoli assault inside the closing stages, but St Juste had other ideas as he stooped to nod in the clinching goal in stoppage time to end a run of eight straight defeats in the competition for Feyenoord.