In the fifth minute Dave Partridge was immediately red carded by Cheshire referee Mike Jones as he attempted to head butt Leon Best as the teams lined up for a corner.
The second sending off was deep in stoppage time when defender Che Wilson - making his debut after a loan move from Southend - brought down Yeovil substitute Ishmael Welsh in full flight.
The early dismissal had a big impact on the game. Brentford gave up all idea of attacking and got as many men as they could behind the ball.
They managed to keep the scoresheet blank at half-time but needed a fair slice of good fortune to do so.
In the 28th minute Wayne Gray was just wide of the far post when Chris Cohen put him through and, when midfielder Cohen again set up Gray on 39 minutes, the striker was just wide again.
Yeovil started the second half brightly and got the winner on 56 minutes with the influential Cohen again involved.
He picked up a pass from Marcus Stewart and crossed from the left for Best to knock in from eight yards.
It was Best's seventh goal in nine starts since joining the Glovers on loan from Southampton.
In the 82nd minute Brentford almost snatched an equaliser. Substitute Calum Willock floated in the ball from the left but the ball struck the Yeovil crossbar before bouncing to safety.
Yeovil should have wrapped things up on 84 minutes when the powerful Best broke through the defence and had only goalkeeper Nathan Abbey to beat but his fierce shot hit the keeper's foot and bounced over the bar.