Charlie Webster scored a brace for Burton on the opening day of the season against Mansfield
Burton Albion climbed off the foot of the League One table as Charlie Webster's late goal stunned fourth-place Cardiff in south Wales.
The Bluebirds had the chance to go back top of League One with victory, and had good chances to take the lead through Yousef Salech and Joel Bagan.
But as the game wore on the frustration inside the Cardiff City Stadium grew, and the Brewers looked more and more off a threat on the counter attack.
And with 82 minutes played, Charlie Webster made the most of a bouncing ball in the Cardiff box to fire past Nathan Trott.
Victory lifts the Brewers to 22nd, one point away from safety, while the Bluebirds miss the opportunity to return to the summit, and instead remain fourth.
Brian Barry-Murphy made five changes to the Cardiff team that beat Wigan on Saturday, and the fresh legs started strongly.
Salech had two close-range headers saved by Bradley Collins, the second of which he would have wanted back after heading straight at the Burton goalkeeper.
The best chance of the first half for the Bluebirds fell to Bagan. Collins could only parry a Rubin Colwill free-kick to the feet of the Cardiff full-back, but his effort from near the penalty spot sailed over the bar.
Burton, who made three changes from 4-0 hammering against Plymouth on Saturday, almost took the lead against the run of play midway through the first half.
Sebastien Revan's corner found a late-arriving George Evans at the back-post, but the Brewers midfielder was denied by an excellent reflex save from Nathan Trott.
At the other end Burton continued to offer reminders of their own threat, and Webster should twice have done better after finding space on the edge of the Cardiff box, instead sending a pair of wild efforts well wide.
The second half started much like the first, and Cardiff should have taken the lead when Salech's cushioned header fell perfectly for Cian Ashford, but the young winger's effort went straight at Collins.
Burton were camped in their own half, but an increasingly frustrated home crowd were crying for those in blue to strike from the edge of the area.
Chris Willock duly obliged on 52 minutes, curling a right-footed effort towards the far corner, but once again Collins was on hand to keep the game goalless.
Barry-Murphy rang the changes on 65 minutes, with Callum Robinson, Ronan Kpakio and Omari Kellyman replacing Ashford, Perry Ng and Wintle.
Robinson almost unpicked the Burton defence, chipping a no-look ball through to Salech, but the Cardiff striker could not make meaningful contact to knock it past Collins.
And with the game seeming destined to finish goalless, Webster landed the knockout blow at the other end, the ball falling to him after a number of ricochets, and the former Chelsea academy player made no mistake on this occasion.
Cardiff return to the Cardiff City Stadium on Saturday, 4 October as they welcome Leyton Orient, while Burton travel to Doncaster Rovers on the same day.
Analysis - League One lessons continue for Cardiff
Tuesday evening looked like the perfect opportunity for Cardiff City to return back to the top of League Two.
Brian Barry-Murphy's side were finally given their 'Welcome to League One' moment when they were well beaten 3-1 by Bradford the last time they played at Cardiff City Stadium.
But on paper this fixture against Burton Albion, who started the day bottom of the league, looked an easier task. It was not.
The Brewers frustrated their hosts for 90 minutes and the additional eight that were added on. It all led to a tense and fractious atmosphere at the full-time whistle.
It is often said that football is a game of fine margins. This game and result epitomised that.
Defeat for Burton would have left them four points from safety before the end of September - albeit with a game in hand over most of their early relegation rivals.
With just six league goals to their name, manager Gary Bowyer, who signed a new two-year deal in June, would have faced increasing pressure.
Instead Cardiff head coach Barry-Murphy has questions that need answering after back-to-back home defeats following what had been such a positive start to the season.
It will not be the last time this season the Bluebirds face a team willing to put 11 men behind the ball and threaten on the break.
If Cardiff are to mount a serious promotion challenge in their first season back in League One, they will need to solve that puzzle sooner rather than later.
Post-match reaction
Cardiff City head coach Brian Barry-Murphy told BBC Sport Wales: "I think when you lose a game of that nature it is pretty sickening from a player and coach's point of view.
"Naturally we are all disappointed, we feel like we created enough chances to win any game, really. When you don't score the goals you feel you should there is always an opportunity for them to score late in the game and they did.
"We created more chances than in any other game this season, but it doesn't really mean anything when you lose, we need to learn how to turn that dominance into wins."
