The midfielder got the decisive touch with his right foot to deflect Romaine Sawyer’s shot from outside the area past the wrong-footed Ivan Lucic in the City goal.
It proved the key moment in a game peppered with scoring opportunities for both teams and one home striker Tammy Abraham will want to forget as he squandered a host of them.
City were forced to replace their goalkeeper after 31 minutes. Frank Fielding appeared to suffer a side strain and 21-year-old Lucic was introduced for his Championship debut.
Fielding had already had plenty of work to do, twice denying Scott Hogan when the striker’s pace took him clear of a pedestrian home defence.
At the other end Brentford keeper Daniel Bentley parried a Luke Freeman shot wide and got a touch to a Joe Bryan header to deflect it wide when the midfielder should have scored.
After Fielding’s departure, Lucic had to go full stretch to save from the dangerous Hogan, while Abraham wasted two good chances for City.
The Chelsea loanee miskicked from Bryan’s low cross and then burst on to a poor back-pass from Romaine Sawyers only to see Bentley save at his feet when he looked favourite to round the keeper.
The second half began with City on top. Abraham clipped the crossbar with a shot from inside the area and Bobby Reid fired wide. Both might have done better.
Then Lucic had to show his mettle again to stop Hogan’s first-time shot following a poor back-pass from Scott Golbourne.
John Egan produced a goal-saving tackle on Abraham as both sides continued to make openings.
Abraham should have put City in front when put clear by Reid’s 66th-minute pass, but he attempted a delicate chip over the advancing Bentley and somehow put his effort wide.
A minute earlier City head coach Lee Johnson had made two attacking substitutions, sending on Lee Tomlin and Gustav Engvail for Marlon Pack and Golbourne.
And it proved over-adventurous as, against the run of play, Brentford went in front.
After Colin’s goal, Egan saw a close range shot blocked by a City defender in a crowded goalmouth.
The home side threw everything forward, but lacked the finishing touch to take anything from the match.