Cardiff slipped to back-to-back home defeats as Charlie Webster’s late goal was enough to snatch struggling Burton a first away win of the season.
Webster turned the ball home in the 82nd minute after the Brewers had seen a succession of shots blocked in the box.
Brad Collins was the busier goalkeeper in the first half, denying Yousef Salech twice in quick succession.
Rubin Colwill forced Collins into another stop after 23 minutes, before Burton came close to the opener when George Evans’ header was saved by Nathan Trott before being cleared by Perry Ng.
Salech had a goal ruled out for a foul on Alex Hartridge before the break, and Collins had to be at his best to keep out Cian Ashford’s fierce drive early in the second half.
Chris Willock saw an effort saved by Collins before Webster won it for the visitors.
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