Qualification for the knockout stage of the Champions League for the first time since 2009 looked a mere formality and two goals from Roberto Firmino and one from Sadio Mane put the visitors comfortably ahead at half-time.
However, in a scenario which mirrored their 2016 Europa League final defeat to the same opposition, they again conceded three after the interval with Wissam Ben Yedder's two goals - including a twice-taken penalty - ramping up the pressure before Guido Pizarro's 93rd-minute equaliser.
"Yes it was not perfect but it's not a general problem
It just happened," said Klopp.
"Could we have done better? One hundred per cent
Do I think it's a mentality problem? One hundred per cent not.
"We opened the door for them, didn't close it, so they could score in the last minute
That's the story of the game."
It cost Liverpool the chance of winning Group E with a match to spare
They now need a draw at home to Spartak Moscow to progress and - although they still lead the table - Sevilla could pip them to top spot as they play already-eliminated Maribor.
Klopp did not use the word complacent but felt his players eased off to give their opponents every encouragement.
"Fantastic first half for us, the second half we made a mistake, we didn't carry on playing football," he added.
"We became passive, they scored the first, then it was obvious the atmosphere changed immediately
That gave them a big boost
"When controlling the game it is not allowed to become passive in a game like this.
"They (the players) are human beings
It was misjudgement."
Sevilla's comeback preserved their year-long unbeaten home record which had looked like crumbling in spectacular circumstances.
Coach Eduardo Berizzo delivered a rousing team talk at half-time and it had the desired response.
"I told them that you had to play with your soul, that there is no mistake that could not be solved," he said.
"They had to go out generating a different energy and people would believe
The team came out and infected 50,000 people,
"We took the risk of going for the game and that speaks of the football bravery of the players."
Source : PA
Source: PA