Leicester City stunned Manchester City at the King Power Stadium in Saturday's late kick-off with a 4-2 victory.
The Foxes struck twice in the opening four minutes through Jamie Vardy and Andy King, while the former grabbed his second after just 20 minutes and third in the 80th minute. Aleksander Kolarov and Nolito scored two late goals to make the score look more respectable.
The reigning champions moved up to 14th, while Pep Guardiola's City slumped to fourth and four points off the top spot.
Before the kick off, Foxes boss Claudio Ranieri insisted his side need to show more title fight if they are to improve, and they showed glimpses of their old-selves with a blitzing opening 20 minutes to ultimately put the game beyond Pep's men.
In terms of team news, Leicester's Kasper Schmeichel had recovered from surgery on a fractured hand, but this game came too soon for him withRon-Robert Zieler starting in between the sticks once more.
Jamie Vardy, Riyad Mahrez, Islam Slimani and Andy King all returned to the starting XI after being rested for the club's 5-0 Champions League loss to FC Porto in mid-week, while Danny Drinkwater missed out through suspension.
For City, Raheem Sterling returned to the substitute bench after recovering from a knock that saw him miss their clash against Burnley, while Yaya Toure was dropped from the starting XI after a mid-week drink-driving charge.
Manchester City's Yaya Toure on drink driving charge https://t.co/Fv72GgJaVG
Sergio Aguero and Fernandinho were replaced byKelechi IheanachoandFernando as the pair begin their respective bans following the loss to Chelsea.
Despite Leicester's ability to surprise, no one could have predicted the start to this one, with the reigning champions scoring two goals in the opening four minutes to shock Pep's side.
Fantastic link-up play between Riyad Mahrez and Islam Slimani saw Jamie Vardy played through in between John Stones and Aleksander Kolarov for the England international to slide home his first goal in 16 games to give them a 1-0 lead.
Less than a minute later, Slimani was involved once more after taking down a long throw on the edge of the box, feeding Andy King for him to curl one into the top corner, with Claudio Bravo only able to flap at it to stun the visitors.
Claudio's men continued to press on a shaky looking City, and Slimani should have made it three after Robert Huth knocked it down from a corner six yards out, but he blasted it over to the shock of the King Power faithful.
And not soon after, it was three, with Vardy netting once more as Leicester looked more like the team from last season. A long 40-yardball from Christian Fuchs found Mahrez, who slotted Vardy through once more with a lovely touchas the striker rounded Bravo and found an empty net.
 Jamie Vardy gets his second of the match to put the champions in complete control. 3-0 (27 mins) #LEIMCI pic.twitter.com/CW4wpqaBu6
Incredibly, Mahrez had a chance to make it four just moments afterwards. Asuccession of step-overs led to shot that was pushed away well by Bravo, but City, and Pep, looked shell-shocked, struggling to even keep hold of the ball.
Guardiola's side began to scrape their way back into the game through some half-chances with set-pieces, but the Foxes continued to defend well andlook dangerous in attack, with Slimani being a nuisance up top.
The second half saw City come out fighting as Leicester sat back to soak up the pressure, with Iheanacho, De Bruyne spurning wonderful opportunities in the home side's box, while IlkayGundogan dragged one just wide of Ron-Robert Zieler's post.
The introduction of Yaya Toure and Raheem Sterlingdid little to improve City's accuracy in front of goal as the game remained open for both sides to attack.
Is that... Yaya Toure, up top?#LEIMCI #MCFC https://t.co/Jyx9EDEpDA pic.twitter.com/7kRlVlFlEk
Vardy then pounced on a loose John Stones back pass to Bravo to round him for a second time and stroke the ball into the net for his hat-trickfrom an almost impossible angle, with Bacary Sagna's clearance ruled to be over the line by goal line technology.
Kolarov bent in a fine free kick to give Pep something to smile about, while Nolito struck from close range,but they weremerely a consolation strikes as City suffered their second consecutive Premier League game.
This is the first time in history a side managed by Pep Guardiola has conceded 3+ goals in back-to-back league games. pic.twitter.com/eIpOGWWD4L
Leicester City line up: Zieler; Fuchs, Huth, Morgan, Simpson; Albrighton, King, Mahrez, Amartey; Vardy, Slimani
Manchester City line up: Bravo; Sagna, Kolarov, Stones, Zabaleta; Silva; Gundogan, Fernando, De Bruyne, Navas; Iheanacho