No wonder Roberto Mancini's head slumped in the Allianz Arena dug-out at one stage. City's Champions League challenge is suddenly in danger of being snuffed out after the first defeat of the season.
The opening draw at home to Napoli was a classic case of settling into this most demanding of competitions, but losing to the German champions means victory is now vital against visitors Villarreal next month.
Two strikes from in-form Germany hit man Mario Gomez before half time erased City's early confidence and leave them vulnerable now in a Group A that was always going to be the toughest ask.
Goalkeeper Manuel Neuer's last meeting with the Blues had resulted in him leaking goals to Benjani and Stephen Ireland in a 2-0 Uefa Cup defeat for his old club Schalke in November 2008.
But after two first-half goals from Bayern's own "Super Mario", City were always facing an uphill struggle against the Bundesliga leaders, who had not conceded a goal in the last nine matches.
Norwich City are the only English team to have triumphed against Bayern in Munich over the years, and that rather bizarre statistic was in no jeopardy once Gomez had snapped up his double.
City, ironically, might have been ahead in the early minutes when David Silva was brought down in the penalty area but the Hungarian referee was having none of it
Although Rafinha fired in a dangerous cross that found no Bayern takers, City looked more than comfortable in those early stages, and their passing and movement caused some concern for the home side.
But Bayern, with a 100 per cent record in their last nine matches, gradually asserted their right as home side to call the shots, and it was often Bastian Schweinsteiger's power shot that ensued.
Ribery caught Hart with a difficult low drive that carried enough venom to squirm from the goalkeeper's grasp and kick high into the air, though no German was close enough to take advantage.
The pacy Frenchman's next break ended with Thomas Muller seeing a shot well blocked by Gael Clichy, and it was becoming apparent that Munch were gradually applying the screw.
And the alarm bells should have been ringning after 36 minutes when City's defence was opened up worryingly easily only for Schweinsteiger to make a pig's ear of a golden opportunity.
Yet barely a minute after he had spooned his near-post effort over the bar, the Blues were caught out at the back once more, and this time were made to pay the ultimate price.
Again Ribery was the instigator, offered the space for a shot that Hart saved but couldn't hold. He saved at point-blank range as Toni Kroos pounced on the rebound, but Gomez tucked away Bayern's third attempt.
That was tough to take, but the real hammer blow came at the end of the half as Gomez followed up Hart's save at the foot of his post from a header to turn in Munich's second
As the tie slipped away from the Blues in the second half, Mancini sent fit-again Nigel de Jong into the fray but it was striker Edin Dzeko who made way, and not with good grace either. Carlos Tevez stayed glued to the bench.
In truth, Dzeko, who gave a wonder performance in the Premier League at Tottenham, had never threatened to repeat that form in the Allianz Arena, but he was not alone in that respect.
City's poorest performance of the campaign by far was summed up when substitute Aleks Kolarov managed the Blues' first shot of the second half with 83 minutes on the clock.