N'Golo Kante's stunning long-range strike earned Chelsea the points and condemned his former side Leicester to defeat.
Alvaro Morata broke the deadlock with his third goal of the season for the Blues after a super Cesar Azpilicueta cross.
The Blues doubled their lead five minutes into the second half through N'Golo Kante, who drilled a low shot from range into the bottom left corner.
Thibaut Courtois gave Leicester a lifeline by tripping Jamie Vardy inside the box and the England striker buried the penalty by striking it powerfully down the middle.
Chelsea rode their luck late on but saw the game out for a third straight victory.
1. ALVARO MORATA ON FIRE
Real Madrid fans must be wondering if their club messed up selling Alvaro Morata after he continued his fine start in Chelsea colours.
Madrid have failed to win their opening two matches at Bernabeu for the first time since 1995 following today's draw with Levante.
But Spanish international Morata can't stop scoring for Chelsea following his £60million summer signing from the Spanish giants. Here he made it three goals in four Premier League matches with a clinical first half header after also scoring as a sub on international duty with Spain in their win over Italy.
2. N'GOLO KANTE SHOWS HIS CLASS
N'Golo Kante was deservedly crowned PFA player of the year last term as he won back to back titles after swapping Leicester for Chelsea.
Leicester players and fans appreciate his talents as much as anyone. And the midfield dynamo underlined his class back at the King Power with a fine low right-foot shot into the bottom corner from outside the box in the 50th minute to make it 2-0.
Ironically it was Wilfred Ndidi, bought to replace Kante, who failed to close him down quick enough as the French ace despatched a fine low finish. Kante also showed his class by not celebrating out of respect to his old club
3. ANTONIO NOT A WOLLY WITH A BROLLY
Blues boss Antonio Conte caught the eye with his touchline theatrics – especially when it started raining heavily.
The Italian donned a baseball hat and a Chelsea overcoat, as well as holding a fluorescent bib. It was quite a sight and at times he appeared to be directing traffic not his players.
But his players got the message loud and clear as Alvaro Morata headed his side infront.
4. Mahrez back on the grid
Riyad Mahrez's location on deadline day remains as mystery as he chased a transfer.
But the 2016 PFA player of the year was most definitely back at the King Power after being given permission to leave Algeria's camp in the international break in an ill-fated bid to get a big-money move.
It was like the title-winning days when Mahrez picked out Vardy with a defence-splitting pass in the 25 minute but the striker's first-time right-foot shot went wide. Mahrez also picked out compatriot Islam Slimani in the first half but the striker's effort was saved
5. Maguire a good investment
Craig Shakespeare said in the build up to this game that the £17million Leicester paid for centre-back Harry Maguire already looks a bargain.
He was referencing some of the other fees being offered elsewhere close to the deadline for other players with just 12 months left on their contracts.
Had City bought Maguire in August rather than June they could have expected to pay a lot more. Maguire has quickly earned an England call-up and looks at home in the Foxes' defence - often stylishly bringing the ball out from the back.