Brendan Rogers' Leicester were looking to start a calendar year with three consecutive league wins for the first time under the Northern Irishman's management. They could go top of the Premier League with a win.
Frank Lampard made four changes to his starting eleven that ran out 1-0 winners at Craven Cottage last week against West London rivals Fulham. The most notable of these being Callum Hudson-Odoi who started over Hakim Ziyech.
The pressure was certainly on for the Blues as kickoff drew near as West Ham's 2-1 victory over West Brom earlier in the evening saw the Hammers go above Chelsea in the league, making this clash a must-win game.
Story of the match
The home side made a dream start as Leicester won a corner early on. A scuffed shot by Harvey Barnes following a cut back fell to Wilfried Ndidi, who hit a bending half volley off the far post and into the net for 1-0.
A stormy-faced Lampard was the scene of the first 15 minutes, but Chelsea started to get into gear as the 20 minute mark neared. Reece James played a give-and-go with Hudson-Odoi, only to have his shot tipped over the bar by Kasper Schmeichel. The following corner was headed straight at the Dane by veteran defender Thiago Silva.
The Foxes didn't succumb to the building pressure and wouldn't lie down for the visitors. Edouard Mendy was called into action a couple more times as the half progressed, saving shots from Mark Albrighton and Jamie Vardy.
Lampard's men looked to have a life line in the 38th minute as Christian Pulisic was brought down by Johnny Evans on the edge of the box - referee Craig Pawson initially gave a penalty but it was overturned by VAR. The free kick taken moments after was blazed over by Mason Mount.
In the minutes following the penalty incident, Leicester made it 2-0. Albrighton's lofted ball into the Chelsea box following a goal kick ended up falling to James Maddison, who tucked the ball past Mendy after peeling away from the sleeping James.
The Blues' players ended the half with a mountain to climb, pressure on their boss's job building.
Judging by the scoreline at halftime, Rogers' side were able to predict how the second half would begin. Chelsea needed to push up the pitch in search of goals, playing right into Leicester's hands.
The home team managed to muster a couple of golden chances either side of an offside goal, which was turned home by Albrighton in the 53rd minute. James Justin missed a free header and Mendy made a splendid save with his legs to deny Youri Tielemans.
Timo Werner and Ziyech replaced Kai Havertz and Hudson-Odoi in an attempt to salvage the game with half an hour to go. Even from a neutral standpoint, both were virtually invisible until the final whistle.
Vardy had a chance to seal the three points late on after substitute Timothy Castagne played a neat ball in behind the Chelsea defence to find the striker, only for Mendy to smother the opportunity.
Late on, the two Chelsea subs combined through a free kick to score a goal, but it was ruled out for offside. Werner was marginally off as he poked the ball past the keeper following a Ziyech delivery.
Lampard "Sacked in the morning?"
Despite Chelsea's unconvincing win against Fulham on Saturday, tonight's loss against Leicester sees Lampard & co fall to 8th in the table, playing to a standard at the moment that fans would undoubtedly brand as unacceptable.
The Chelsea boss, who is in the middle of his second campaign with the club, has been scrutinised by the press and fans due to a diabolical run of form - many calling for his sacking.
If the young manager isn't sacked in the next few days, then surely anything but a win against Luton in the FA Cup on the weekend will result in the second Premier League sacking of this season.
The players (especially his new signings) look unmotivated and clueless, perhaps suggesting a new footballing brain at the helm would be able to repay the grand sums of money owner Roman Abramovich has injected into the club as of recent. This evening, Chelsea suffered their fifth defeat in eight games.
A deserving Leicester top the PL table
The Foxes didn't allow history to repeat itself tonight, as the visitors held a strong record when visiting the King Power in recent years and were very strong both offensively and defensively.
The home side allowed Chelsea to come on to them in the second half, calmly soaking up pressure and breaking down the other end of the field with dangerous counter attacks, forcing keeper Mendy to be the Blues' most productive player of the game.
Leicester are having a purple patch of form that Chelsea fans will be no doubt jealous of - a tactically strong manager getting the most out of his players and scaring league and European defences with clinical attacking.