Now, with Ranieri gone and Craig Shakespeare in charge, Leicester have been transformed, and they were on their way to another spectacular triumph when captain Wes Morgan bundled them into a first-half lead.
It continues a fairytale 12 months for Leicester following their Premier League triumph last season.
“I’m not sure if it will happen again but we did it,” Morgan told BT Sport.
“We proved a lot of people wrong and pulled off the impossible again.”
It put Leicester in control of the tie, a supremacy they emphasized when Marc Albrighton drilled home a second nine minutes after the interval, seconds after Sergio Escudero hit the bar for the visitors.
Leicester survived a frantic final spell when Samir Nasri picked up a second yellow card for a clash of heads with Jamie Vardy – who missed two great chances – keeper Kasper Schmeichel saved a penalty from Steven N’Zonzi that could have taken the tie into extra time and Sevilla boss Jorge Sampaoli was sent to the stands as tensions reached boiling point.
The victory means the Foxes join the illustrious company of Barcelona, Bayern Munich, Borussia Dortmund, Juventus and Real Madrid in Friday’s quarter-final draw.
On Wednesday, Manchester City go to Monaco and Atletico Madrid play Bayer Leverkusen to determine the final two sides in the last eight.