There was no upset to the form guide as in-form Brentford brushed City aside before half-time on a boggy pitch at Griffin Park.
Former Bees defender Karleigh Osborne briefly had the Robins on level terms after the hosts had benefited from an early Aden Flint own goal.
All that was inside the first 12 minutes, but the Sky Bet League One leaders were back in front when Alan Judge’s shot crept over the line after what originally looked like an excellent save from Elliott Parish.
When Marcello Trotta added a third just before the break, it seemed a question of how many Brentford would end up with.
City stuck to their task, matching the table toppers for periods of the second half, but never really threatened an unlikely comeback.
Steve Cotterill gave a first start to Tyrone Barnett up front, as Jay Emmanuel-Thomas was dropped to the bench for the first time in a league game all season.
Also among the substitutes were Bobby Reid, who made way for Marlon Pack, and new loan recruit Wade Elliott, signed only a matter of hours before kick-off.
Within three minutes of the first whistle, Simon Gillett was in the book for a startlingly late lunge on Shaleum Logan – although the midfielder’s defence to blame the slippy playing surface may well have had some substance.
For the third successive away league match, City found themselves behind before having time to settle into their new surroundings.
It was another to add to the ‘preventable’ category too, as Jake Bidwell’s cross from the left looked destined for the expectant grasp of Parish before Flint intervened to slice the ball into his own unguarded net.
It was a bitter blow for the visitors to take so early on against a team as high on confidence as Brentford, but the response was instant.
Flint had already threatened to make amends with a downward header into the sidenetting before Marvin Elliott won the ball in midfield and Simon Gillett released Osborne in acres of space on the right.
With no red and white shirt taking it upon themselves to close him down, the defender kept going before planting a well-struck low shot into the far corner of the net from 20 yards.
It was to prove his last action on his return to Griffin Park, seemingly injuring himself in the process of striking the ball. Brendan Moloney took his place.
The hosts were stunned, and City nearly took further advantage when Flint’s knockdown presented a glorious chance to Barnett, who could only drag his shot inches wide of the post as the ball dropped.
The Robins were undoubtedly holding their own, but a slick team move unhinged them in rather more stylish fashion on 25 minutes.
When the ball was played into the feet of Marcello Trotta, Judge’s clever run from deep offered the striker an option for a backheel which totally outfoxed the City defence.
As Judge stepped inside and hit a vicious shot from 15 yards, Parish looked to have made a stunning save, but instead only succeeded in parrying the ball into the air before it dropped almost apologetically into the net behind his dive.
This time Brentford had a lead they were not prepared to surrender cheaply.
Instead they were intent on increasing it, as Clayton Donaldson eluded the offside trap to bear down on goal only for Parish to make a good save.
And three minutes before half-time the Bees had their third. Judge was forced wide inside the penalty area but still found the perfect cutback for Trotta to convert from eight yards. It was simple stuff.
Cotterill’s response was to hand Wade Elliott his City debut before a ball was kicked after the interval, withdrawing Pack.
The midfielder’s first contribution was to add his name to the book with an ill-timed tackle on Alan McCormack.
It was to prove a second half to forget as a spectacle. Emmanuel-Thomas was given 25 minutes to produce a couple of pieces of magic but was unable to do so in difficult conditions.
Barnett had City’s best opening, cleverly rolling his man before blasting over the crossbar from the edge of the box, but it was a night to forget for Cotterill’s men.