Robert Huth scored twice as Leicester sensationally thrashed title favourites Manchester City 3-1 to continue their remarkable challenge for the Barclays Premier League crown.
Riyad Mahrez also got on the scoresheet as the Foxes tore into their illustrious hosts at the Etihad Stadium, destroying the feelgood factor created by the announcement of Pep Guardiola's summer arrival.
Sergio Aguero headed a consolation in the closing minutes but City were already well beaten.
Quadruple-chasing City had hoped to pull level with Claudio Ranieri's men at the top of the table but instead ended the day trailing them by six points.
Manuel Pellegrini wanted news of his imminent departure made public partly in the hope it could galvanise the team for the rest of the season, but on this evidence it had the opposite effect.
Leicester, unheralded at the start of the season, attacked with speed and energy throughout and looked a class above City.
The warning signs were evident from early on and Leicester never allowed City's vulnerable central defensive duo of Martin Demichelis and Nicolas Otamendi to settle.
They caught the hosts napping as they snaffled their first opportunity with three minutes gone.
A Mahrez free-kick bounced through the area from the right and Huth was the quickest to react six yards out. Demichelis tried to get his body in the way of the German's flicked shot but succeeded only in diverting it past the helpless Joe Hart.
City were ragged and things could have got considerably worse as they were pulled apart continually in the opening 20 minutes.
Hart needed to be alert to smother an effort from Jamie Vardy and was then quick off his line to deny Danny Drinkwater after another quick counter-attack. Shinji Okazaki also narrowly failed to turn in a dangerous cross from Vardy.
City did offer some brighter moments in attack and they were perhaps just millimetres away from being awarded a penalty as Pablo Zabaleta was ruled to have been fouled by Christian Fuchs just outside the box.
But too often City's pressure failed to result in chances that threatened Kasper Schmeichel's goal. Yaya Toure blasted over and David Silva guided an effort wide. When Aguero did find the target, Schmeichel was in the right place.
City needed to find an extra gear but it was Leicester who upped the tempo and they doubled the lead with a brilliant Mahrez goal early in the second half.
The Algeria international picked up the attack after a break by Wes Morgan and skipped over a challenge from Otamendi. He then wrong-footed Demichelis before firing a blistering shot past Hart.
City briefly roused themselves as Schmeichel kept out a powerful header from substitute Fernando but Huth sent the visiting fans into dreamland by heading the Foxes' third on the hour. The former Chelsea defender rose above Demichelis and Aleksandar Kolarov to head into the top corner from a corner.
That goal killed off all hope of a City revival and Leicester continued to boss the game.
Vardy went close to adding a fourth with a shot that curled just wide.
Aguero did pull one back by heading in a Bersant Celina cross three minutes from time but the game was already up.
TWEET OF THE MATCH
"The Huth? You can't handle the Huth! #believe @LCFC @robert_huth" - defender Christian Fuchs' post after Leicester's win, accompanied by a photo with two-goal hero Robert Huth
Joe Hart: 7
Pablo Zabaleta: 6
Martin Demichelis: 4
Nicolas Otamendi: 4
Aleksandar Kolarov: 5
Fabian Delph: 7
Yaya Toure: 5
David Silva: 6
Raheem Sterling: 6
Sergio Aguero: 7
Fernando (for Toure, 51) 5
Kelechi Iheanacho (for Delph, 51) 5
Bersant Celina (for Silva, 76) 5
Kasper Schmeichel: 7
Danny Simpson: 7
Wes Morgan: 8
Robert Huth: 9
Christian Fuchs: 7
Marc Albrighton: 7
Danny Drinkwater: 7
N'Golo Kante: 8
Riyad Mahrez: 9
Jamie Vardy: 7
Shinji Okazaki: 7
Leonardo Ulloa (for Okazaki, 80) 5
Demarari Gray (for Mahrez, 76) 5
Nathan Dyer (for Albrighton, 85) 5
Riyad Mahrez's stunning goal may take the plaudits but Robert Huth was a match-winner at both ends - shackling City's expensive front line and coming up with the two goals required to maintain his side's unfolding miracle.
MOMENT OF THE MATCH:
When Mahrez turned Demichelis and Otamendi inside-out and struck the second, it was the moment that underlined once and for all that Leicester are genuine title contenders.
VIEW FROM THE BENCH:
From Huth's third-minute opener onwards, things could hardly have gone any better for Claudio Ranieri, who must continue to pinch himself. On this showing, few could blame Manuel Pellegrini if he wished to hasten his summer exit.
MOAN OF THE MATCH:
City's fans did not exactly embrace the magnitude of the first versus second showdown. There were plenty of empty seats at the start and swathes of blue on all four sides by the time Aguero grabbed his late consolation.
Manchester City v Tottenham (Barclays Premier League, February 14)
Arsenal v Leicester (Barclays Premier League, February 14)
Leicester boss Claudio Ranieri had plenty of praise for his players, telling BT Sport 1: "We know we had to concede possession because they (Manchester City) have very good players.
"But we were never afraid. We wanted to win here with a fresh mentality. Also we scored so early, it's not easy to maintain concentration. But we were concentrated because we respect City a lot.
"Now it's important to recover well because we spent a lot of energy. Sometimes we run more than the ball!
"We play every match (like) it is the last match. Now we are very, very confident. It's important to think about Arsenal. Another amazing team, fantastic players, but we are ready. Our fans are dreaming and that is fantastic."
Man of the match Robert Huth said: "We expected them to come out (at us). But for the first five, 10 minutes we came out better. A job well done.
"Certainly all teams that are in the Champions League. Europa Cup (sic), it's inevitable that they're thinking of other games, it works in our favour. We haven't really talked about anything but the next game."