The Clarets had not one, but two goals ruled out by VAR, while the Bees’ late winner came deep into stoppage time.
Scott Parker’s side had earlier launched a remarkable comeback to fight back from three goals drawn to level at 3-3.
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But Mikkel Damsgaard’s 94th-minute strike inflicted a painful defeat.
Here’s how Burnley’s players rated:
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1. Martin Dubravka - 5/10
Hard to give him a 6 or higher when he’s conceded four goals. Has to show more domination of his box. (Photo by Molly Darlington/Getty Images) Photo: Molly Darlington
2. Josh Laurent - 5/10
Feel sorry for him in some way, a victim of his own flexibility. Taken off at half time after being used as both a wing-back and in central midfield. Photo: Kelvin Lister-Stuttard Photo: Kelvin Lister-Stuttard
3. Bashir Humphreys - 6/10
Another one that was popping up all over the place. Did okay, whether in the back three or at right back. (Photo by Matt McNulty/Getty Images) Photo: Matt McNulty
4. Joe Worrall - 5/10
Allowed Thiago to get down the side of him for Brentford’s second. Lack of pace was exploited in behind by Brentford. Photo: Kelvin Lister-Stuttard Photo: Kelvin Lister-Stuttard