Brentford's nine match unbeaten run came to an end at Cardiff as two first-half goals condemned Dean Smith's side to defeat.
Joe Ralls gave the Bluebirds an early lead as the west Londoners failed to deal with the second ball from a long throw.
Yoann Barbet had a good chance to level soon after but he fired over from a well-worked free kick from Ollie Watkins.
The Bees should have been on level terms just after the half hour mark but what transpired was one of the worst misses you will ever see at a professional contest.
Watkins had brilliantly won the ball back and taken the ball past Neil Etheridge by squaring for Neal Maupay.
The Frenchman had the goal gaping with Sol Bamba racing to the line and, even though he could have walked it into the net inexplicably fired wide.
To compound the horrendous miss, Bruno Manga broke down the right and his cross found Danny Ward who slid the ball home.
Brentford pushed hard in the second half but failed to breach Etheridge's goal, with Lasse Vibe and Sergi Canos going closest as they had their efforts cleared off the line.
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