Leicester returned to the top of the Barclays Premier League with a 2-1 victory on Monday night as Chelsea's desperate defence of their crown continued.
The irrepressible duo of Jamie Vardy and Riyad Mahrez once again scored Leicester's goals to send them two points clear at the summit and inflict a ninth league loss of the season on the champions, leaving Jose Mourinho's men 20 points behind and only one point above the relegation zone.
The meeting was in stark contrast to the last clash between the sides at the King Power Stadium at the end of April when a 3-1 win put Mourinho's side on the brink of the title and left the Foxes' survival hopes in the balance.
As has been the case so far this season, Leicester looked inspired and Chelsea jaded and lacking imagination.
Mahrez got the home fans off their seats in the second minute with a mazy run in-field from the right before forcing Thibaut Courtois to get down to his left to smother his shot from just outside the area.
Wes Morgan's sliding challenge to block a goal-bound effort from Eden Hazard was timely but moments later Leicester were dealt a blow when Danny Drinkwater hobbled off holding his hamstring. He was replaced by former Chelsea schoolboy Andy King.
Mahrez worked Courtois again in the 18th minute after bringing down the ball on the edge of the area, but once more it was a routine save for the Belgian.
It was Chelsea's turn to make an enforced change after half an hour when Hazard appeared to hurt his hip after going to ground under a challenge from Vardy. Mourinho introduced Pedro.
Vardy's next involvement would hurt Chelsea further. Mahrez spotted the striker's clever front-post run and found him with a lovely curling cross from the right which Vardy dispatched first time on the volley to give Claudio Ranieri's side a 34th-minute lead.
During a week when Walkers released a special edition flavour called 'Vardy Salted' in homage to the 28-year-old, it was certainly a crisp finish.
Chelsea were almost level immediately as Nemanja Matic's header from a corner clipped the top of the crossbar on the way over.
Marc Albrighton tested Courtois with a curling effort just before half-time and it was his superb deep cross from the left flank at the start of the second half that set up Mahrez for the second goal.
The little Algerian's first touch to bring the ball under his spell was instant. He then turned Cesar Azpilicueta one way then the other until he had the yard of space he needed to bend the ball around Courtois and into the far corner of the net.
The King Power was rocking but it was nearly silenced twice either side of the hour mark when Pedro was crowded out in a goalmouth scramble before Kasper Schmeichel diverted Diego Costa's shot over the bar when the Chelsea striker was through on goal.
Mourinho threw the dice and brought on Cesc Fabregas and Loic Remy, with John Terry and Oscar making way, and two of his substitutes combined to get the visitors back in the game after 77 minutes as Remy headed home Pedro's cross from close range.
Remy sent a shot wide from the edge of the area but the champions could not force an equaliser despite some late pressure.
It was Chelsea's first defeat to Leicester since February 2001. The man in charge of the London side that day? Current Leicester boss Ranieri.
TWEET OF THE MATCH
"YES! If Leicester win the @premierleague I'll do the first MOTD of next season in just my undies." Leicester-born former striker Gary Lineker is still not convinced the Foxes can lift the title.
Kasper Schmeichel: 7
Danny Simpson: 7
Wes Morgan: 8
Robert Huth: 7
Christian Fuchs: 7
Danny Drinkwater: 6
N'Golo Kante: 7
Marc Albrighton: 7
Riyad Mahrez: 9
Leonard Ulloa: 6
Jamie Vardy: 8
Andy King 6
Gokhan Inler 5
Shinji Okazaki 5
Thibaut Courtois: 6
Branislav Ivanovic: 5
Kurt Zouma: 6
John Terry: 6
Cesar Azpilicueta: 5
Nemanja Matic: 6
Eden Hazard: 5
Diego Costa: 6
Cesc Fabregas 6
Loic Remy 7
RIYAD MAHREZ: The Algerian is a little magician. He tormented Chelsea's defenders all evening and provided a lovely, inch-perfect cross for Vardy to open the scoring. Mahrez then got his name on the scoresheet with a touch and goal that was almost Bergkamp-esque.
MOMENT OF THE MATCH
The move for Leicester's opening goal was a thing of beauty. Good play from Kante, a clever run from Vardy, a brilliant cross by Mahrez and a stunning finish. If Barcelona had scored that goal it would be replayed over and over.
VIEW FROM THE BENCH
Ranieri cheered each Leicester goal and looked emotional as the final whistle blew at the end of five added minutes to signal victory for his team. Mourinho congratulated the man he succeeded as Chelsea boss back in 2004 with a warm embrace but the Portuguese must be worried about his side's plight.
MOAN OF THE MATCH
Just what has happened to Chelsea? Their fall from grace this season is remarkable and it shows little sign of abating. Mourinho's men lack inspiration and imagination and are stuck firmly in a rut they can't get out of.
WHO'S UP NEXT
Everton v Leicester (Barclays Premier League, Saturday, December 19)
Chelsea v Sunderland (Barclays Premier League, Saturday, 19 December)
Mourinho felt "betrayed" by his players after Leicester scored from two situations he had warned about.
"I think they deserved to win because they were better than us during a long period of time," he told Sky Sports 1.
"We conceded two goals that were unacceptable. One of my best qualities is to read the game for my players and I feel like my work was betrayed.
"All last season I did phenomenal work and brought them to a level that is not their level and more than they really are... or this season we are doing so bad."
On Hazard's injury, the Portuguese said: "In 10 seconds, Hazard made the decision to come off himself. It must be something serious."
Asked if Chelsea were out of the race for the top four, he replied: "Yes, clearly."
Ranieri said: "We had a fantastic one hour and the last 30 minutes we suffered a lot. But they are the champions and we had to suffer to win the match.
"All the players believe in and help each other. Only in this way can you win against big champions.
"I told the players we need another five points (to stay up). I put a target of 40 points at the beginning of the season and when we achieve this we change the target.
"I think about how we can improve. They are very, very calm and have to improve a lot.
"It's a magical time, but we must continue to work hard. I don't want to wake up, I want to continue to dream with our fans."