Swindon nearly took an early lead after a cross from Ricky Shakes found Chris McPhee whose diving header was only just saved by the Brentford 'keeper.
Both sides had more chances to score before Brentford took the lead on 27 minutes when Paul Booker started a run in his own penalty area, and ran over 70 yards with the ball before scoring from 10 yards out.
Swindon had a goal disallowed on 30 minutes with a shot from Benjamin, but it had already been ruled out before crossing the line after a foul by McPhee so Brentford were instead awarded a free kick.
Marcus Gayle then made it 2-0 from close range on 39 minutes, and play was then held up for a couple of minutes as a Swindon fan appeared on the pitch from the Town End and ran up the pitch before being caught by Rhys Evans and handed up to the stewards and Police. A £1000 fine for him will make it an expensive day out.
A free kick from Andy Gurney went close, but just over the bar and Swindon went into the half time break losing 2-0.
In the second half Diagouraga replaced Whalley and Aaron Brown replaced Paul Smith.
Swindon then had two penalty appeals turned down in as many minutes. The first was for a hand ball in the box, then Cureton was fouled in the box, and both times the referee was play on. Andy Gurney was also booked for protesting too much about this.
Jamie Cureton can close for scoring for Swindon, and then in the 70th minute Swindon were awarded a free kick just outside the box. Aaron Brown took the kick and scored making it 2-1, but it was too little too late fro Swindon.
On 75 minutes Brentford made it 3-1 with a lob from Calum Willock going over the head of Rhys Evans into the back of the net.
Brentford came close to making it 4-1, but this late effort was saved by Rhys Evans, and Swindon ran out of time before they could score any more goals themselves.
Overall a fairly average game in which both sides had plenty of chances. This defeat looks set to seal Swindon relegation to League Two unless they win their next two games against Bristol city and Huddersfield, and the sides above them including Milton Keynes, Rotherham, Tranmere and Hartlepool all lose.