Goals from Erling Haaland and Mateo Kovacic inflicted defeat on Enzo Maresca in his first match in charge of the Blues.
City were shorn of all four of their Euro 2024 finalists -- Rodri, Kyle Waker, John Stones and Phil Foden -- from the start as Guardiola opted to give them extra time off to recover from their summer exertions.
The likes of Kevin De Bruyne, Bernardo Silva, Ruben Dias and Manuel Akanji did play the 90 minutes despite their late return to training after reaching the knockout stages of the Euros.
Yet, the champions were still able to lay down a marker against one of the few sides they failed to beat in the league last season.
"I really didn't expect it. I know what these guys can do, but the first day and lack of training," said Guardiola.
"We had two or three days to prepare, but we solved this lack of many things with our commitment.
"You cannot imagine how privileged and fortunate I am to live these experiences with this incredible group of players."
Maresca has the tough task of moulding a functioning team unit from a bloated Chelsea squad that has 43 players and over 50 on the books including those on loan.
Sterling axed
The consequences of those difficult decisions played out even before kick-off as Raheem Sterling's camp released a statement expressing his dismay at being left out of the matchday squad.
Ben Chilwell was another to face the cull, while Conor Gallagher and Romelu Lukaku are among those not to have been handed squad numbers.
None of Chelsea's nine summer signings to date were included in Maresca's starting line-up.
Even more surprisingly, Enzo Fernandez was named captain despite being embroiled in a race row for a post on social media after Argentina's Copa America victory last month.
City, by contrast, are a model of continuity and consistent excellence.
Haaland was one of City's few stars to have had a summer off from international tournaments and took just 18 minutes to make his mark.
Jeremy Doku's low cross was deflected by Bernardo Silva into the Norwegian's path and he coolly dinked over Robert Sanchez.
But Chelsea ended the first half in the ascendency and should have been level before the break.
Ederson spilled Cole Palmer's tame shot but was bailed out by Nicolas Jackson's straying needlessly offside before he turned in the rebound.
Foden was forced into action earlier than Guardiola would have hoped at half-time as the lively Savinho was forced off injured on his Premier League debut.
The lack of pre-season minutes for many on show was apparent in the more pedestrian pace than normal for a major Premier League clash.
Chelsea did most of the pressing for an equaliser but offered City chances to extend their lead in doing so.
"I think we competed very well for much of the game. We were similar if not better," said Maresca.
"The performance was there but we didn't take the chances. Probably the big difference was inside the box."
Sanchez made a fine save to deny Haaland a second goal but the Chelsea goalkeeper was at fault for the strike that sealed their fate.
Kovacic was allowed to burst through the midfield unchallenged and took aim for the top corner, which he found thanks to a weak hand from Sanchez.
