James Hanson scored twice as Bradford maintained their 100% home record and handed 10-man Brentford their first league defeat of the season.
Bees goalkeeper David Button was sent off for a foul on Nahki Wells before Hanson slotted home City's opener.
Wells made it 2-0 with a tap-in after substitute keeper Jack Bonham charged out and Tony Craig's header passed him.
Headers from Garry Thompson and an unmarked Hanson secured the win before Clayton Donaldson hit a Bradford post.
VIEW FROM THE DRESSING ROOM
Brentford manager Uwe Rosler told BBC London 94.9:
"I think everything worked well. We looked decent, we had just started to play again, and then we gifted them.
"For me it was not a red card, but obviously three out of the four goals were presents from us.
"I told the players that when they don't get the second goal, I think we will get a point at least. I knew the longer the game will go when they don't get the second goal, they will get nervous, they try to protect their lead more instead of attack."