Liverpool surrendered a three-goal half-time lead to draw at Sevilla and squander the chance to reach the knockout round of the Champions League with a game to spare.
The Reds appeared on course to reach the last 16 for the first time since 2009 thanks to a brace from Roberto Firmino and Sadio Mané's header, which put them in command after 45 minutes at the Ramón Sánchez Pizjuán Stadium.
But for all Liverpool's attacking prowess, their good work was undone by poor defending in the second half as two goals after the break from Wissam Ben Yedder - one a penalty - set up a tense final 30 minutes.
Guido Pizarro poked home in the third minute of added time as the hosts snatched a draw in incredible circumstances.
That means Liverpool need to beat Spartak Moscow in their final group game in two weeks' time in order to finish top of Group B. Defeat would almost surely consign them to the Europa League with Sevilla taking on Maribor.
Two changes for visitors
Joe Gomez returned to the Liverpool side, making his first European appearance at right-back - over Trent Alexander-Arnold - since the 2-2 draw between the clubs at Anfield back in September.
The only other change from the side which beat Southampton 3-0 at the weekend saw Loris Karius replace Simon Mignolet in goal.
Reds fly out the blocks in Seville
It took Liverpool only one minute and 22 seconds to ignite the game into life when a Philippe Coutinho corner was flicked on at the near post by Gini Wijnaldum.
Wijnaldum's header fell to Roberto Firmino, who squeezed in at the far post with a left-footed effort that Sergio Rico could not keep out, handing Liverpool the ideal start in Andalusia.
The Spanish giants overcame their setback and finally grew into the game. They had the majority of possession in the first half and their endeavour was nearly rewarded when Éver Banega robbed the ball from Jordan Henderson and slotted in Nolito.
He danced round Joe Gomez superbly only to have his shot saved magnificently by Loris Karius, who got down quickly and with a strong wrist diverted the shot on to the post in a show of his ability to manager Jürgen Klopp.
The hosts came agonisingly close again moments later when Ben Yedder was put through for a one-on-one, but the Frenchman pulled his shot horribly wide as another chance went begging for Eduardo Berizzo's side.
Liverpool run riot with quick-fire goals
Liverpool's second was almost identical to the first. A Coutinho corner from the right was flicked on, but this time by Firmino at the edge of the six-yard box, and buried by the unmarked Mané with a diving header at the far post.
The third goal, what seemed like the killer blow to Sevilla, came from poor defending. The former three-time successive Europa League champions allowed a long ball up the left to be snaffled out by Mané.
The winger left Clément Lenglet and Johannes Geis for dead, hurtled into the box and shot at Rico who parried the ball into Firmino in the middle of the area. The striker, left in acres of space, fired into the empty net to put the visitors in touching distance of the last 16.
Ben Yedder pulls one back for hosts
Berizzo must have given the half-time talk of his life as his Sevilla troops looked a different side to the team that surrendered too easily to the Liverpool attack in the first half.
Ex-Sevilla defender Alberto Moreno gave a free-kick away on the edge of the area with a needless challenge that led to Sevilla's first goal.
Banega delivered an inch-perfect cross that met Ben Yedder, who lost his marker, to flick in an excellent header and give the hosts a glimmer of hope.
Sevilla strike from spot to ignite extraordinary comeback
Five minutes later, referee Felix Brych pointed to the spot when Moreno - enduring a nightmarish return to his previous club - trod on Ben Yedder's foot.
The striker went down in instalments but was awarded a spot-kick thanks to assistant behind the goal. He stepped up to convert the spot-kick himself, but the ref ordered a re-take after encroachment.
Yet Ben Yedder rolled the re-take into the bottom left corner - having put the original in the right - as the home side reduced the deficit to just a single goal.
Moreno, who had a hand in both Sevilla goals, was substituted three minutes later with the Reds were quivering at the hosts' fight-back as in an electric atmosphere.
Stoppage-time goal makes the impossible possible
Liverpool might have put the game out of sight at 4-2, with Mané denied a penalty and then substitute James Milner rolling a cross across the face of goal which needed only a touch to be converted.
But the goal that crushed the hearts of all the travelling Liverpool fans came from a corner deep into stoppage time. Geis, with time ebbing away, had a shot from 25 yards blocked by Ragnar Klavan.
From the resulting corner, Klavan met Banega's delivery but put it only out to Pizarro, who trapped it with his right foot and swiped in a half-volley with his left.
That led to Istanbul-like scenes only in reverse order, with Liverpool squandering a three-goal advantage for the first time since May 2014. They must avoid defeat in their final group game to ensure an embarrassing failure to progress.