Maribor’s added-time equaliser against Spartak Moscow opened the door not only for Liverpool to qualify with a match to spare but win the group outright.
They did not so much as walk through as blow it off its hinges with a scintillating first half of football.
They then spent the next 45 minutes desperately trying to barricade the hole they left behind as the half-time introduction of Franco Vazquez sparked Sevilla into life.
It means Liverpool need a point at home to Spartak to now qualify but Sevilla could snatch top spot as they play already-eliminated Maribor.
Liverpool cannot afford another Jeckyll and Hyde performance like this one.
The difference between the two halves was stark as just 90 seconds had passed when Georginio Wijnaldum flicked Philippe Coutinho’s corner to the far post where Firmino stabbed home.
A stunned Sevilla side would have been level had Sergio Escudero not fired into the side-netting instead of crossing and then Loris Karius, goalkeeper for European games only, produced a brilliant fingertip tap to divert Nolito’s shot onto the far post - from where it rolled back across goal before being cleared.
Liverpool heeded the warnings and stepped up a gear with Jordan Henderson putting Firmino through only for the Brazilian to disappoint with his finish allowing Sergio Rico to turn the shot behind.
The save proved academic as what followed was a virtually identical Coutinho corner, this time flicked on by Firmino for Mane at the far post.
On the half-hour Mane was sent flying down the left leaving defenders trailing in his wake and when his shot was parried Firmino tapped into an empty net, the easiness of the goal matched only by the Brazilian’s cheekiness in converting while looking the other way.
The game seemed out of sight and the in-form Salah should have left no room for doubt just before the break when Coutinho reproduced an almost carbon-copy of the pass which led to the Egyptian’s second goal against Southampton on Saturday only for the winger, who matched it with a similar run, but lacked the finish this time.
Eighteen months ago Liverpool held a slender half-time lead in the Europa League final but capitulated to lose 3-1 and there was a sense of history repeating itself as Ben Yedder struck twice.
As in the European final in Basel Alberto Moreno, returning to his former club, was most culpable as he was responsible for both fouls allowing Ben Yedder to head in a near-post free-kick and then tripping the Sevilla striker to allow him to score a re-taken penalty.
The Spaniard was unceremoniously hauled off with Coutinho as James Milner, reprising last season’s left-back role, and Emre Can were sent on to steady a rapidly-sinking ship only for Pizarro to nick a point at the death.
Liverpool manager Jurgen Klopp said: “We stopped playing football in the second half. We have one real weapon — playing football — and we didn’t do that in the second half before we conceded the second goal.
“It was absolutely OK that we were confident after that first half. It’s obvious what we did — the real problem is we stopped playing football. Our main mistake was that for 15 minutes we didn’t play football, we were passive, we were a little bit too deep. They fought back and well done to them.
“It feel like we lost but we didn’t lose. There is a game to go and it’s still in our hands but at the moment it feels really bad.”
Liverpool captain Jordan Henderson added: “I am not sure (how the collapse happened). The first half was very good, disciplined, score good goals. The second half was very bad, we did not start well at all. We gave a corner away and struggled from then on.
“We stopped playing football and did not get the ball to the front three to cause them problems. it does not feel good.
“The message at half-time was to keep going and they were going to give it a right go, they had nothing to lose and we could not cope with it. At least it is still in our hands to top the group.”
Sergio Rico, Mercado, Geis, Lenglet, Escudero, Nzonzi (Vazquez 46), Banega, Pizarro, Sarabia, Ben Yedder (Correa 81), Nolito (Muriel 72).
Karius, Gomez, Lovren, Klavan, Moreno (Milner 63), Wijnaldum, Henderson, Coutinho (Can 63), Salah (Oxlade-Chamberlain 86), Firmino, Mane.
Felix Brych (Germany).