A seismic shock was on the cards when Elijah Adebayo towered above the Citizens defence to head home on the stroke of half time, but quickfire strikes from Bernardo Silva and Jack Grealish denied the Hatters a momentous win over Guardiola's side, who subjected the hosts to successive heartbreaking home losses after their midweek Arsenal agony.
To the delight of the Kenilworth Road crowd and the dismay of fantasy football managers, City talisman Erling Haaland was nowhere to be seen, having sustained a foot injury during their midweek loss to Aston Villa.
Despite the absence of the Scandinavian sensation, a City side with several wrongs to right asked questions of the Luton backline straight away, and Phil Foden tested Thomas Kaminski's gloves from a tight angle in the second minute before Bernardo Silva fired the rebound wide.
The pattern of the first half was established then and there, but Kaminski stood strong in the Luton goal, parrying a fierce Rodri drive away in the 19th minute and also thwarting Phil Foden's low effort from range eight minutes later.
Luton received plenty of encouragement from their dogged defensive display and soon worked up the courage to attack the City backline, firstly seeing Andros Townsend fire a long-range strike straight down Ederson's throat in the 33rd minute.
The former Everton and Crystal Palace man instead turned provider for Adebayo in first-half injury time, picking out the marksman with a brilliant cross to the back post, and Adebayo easily out-jumped Ruben Dias to power a close-range header into the back of the net.
The 25-year-old demonstrated his aerial supremacy for the second successive game, having also nodded in one of the Hatters' three strikes against Arsenal, but a vexed Pep Guardiola had some choice words for fourth official Craig Pawson as both teams headed into the dressing rooms; potentially about the two foul throws his side were penalised for.
The Catalan coach's mood would not have been improved in the 59th minute, as a few half-hearted appeals for a penalty were waved away before Kaminski produced a sensational fingertip save to tip Ruben Dias's first-time effort onto the crossbar, but City's reprieve would soon arrive.
Three minutes after Dias's attempt was stopped, Rodri sauntered into the Luton area and ran into Tom Lockyer, but the ball dropped kindly for Silva, who immediately curled a beauty of a strike into the bottom corner to bring City back on level terms.
Another three minutes came and went before the treble winners completed the turnaround, as Teden Mengi tried to hack Julian Alvarez's ball to the back post clear but failed, and Jack Grealish powered home the visitors' second through the legs of Kaminski.
Luton fans and players remonstrated with referee Tim Robinson about a possible handball offence from Alvarez in the build-up, but replays showed that the ball hit the Argentine's chin as Luton failed to play out from the back.
Rob Edwards's side did not lose any shred of belief, though, and Ross Barkley fired just wide of Ederson's goal in the 68th minute after some nifty footwork, although Jacob Brown was perhaps fortunate to escape a sending-off after wiping out Phil Foden with both feet off the ground.
More to follow.