Match ends, Cardiff City 1, Burton Albion 2.
Burton inflicted the first defeat of the season on Championship leaders Cardiff City in an EFL Cup second-round tie between two much-changed teams.
Tom Naylor put the Brewers in front in the first half after the hosts failed to clear a corner.
Burton doubled their lead with Ben Fox's glancing header after 70 minutes.
Lee Tomlin's cross from a free-kick crept in at the back post to halve Cardiff's deficit, but their late push for an equaliser was in vain.
Four league wins from four - including an opening victory at Burton - had put Cardiff top of the Championship table, and their manager Neil Warnock demonstrated where his priorities lay by making 10 changes from Saturday's triumph at Wolves.
Burton made seven changes of their own from Friday's league win over Birmingham, and it was one of the surviving four, Naylor, who gave them the lead with a calm, low finish after 26 minutes at Cardiff City Stadium.
The visitors were coasting to victory when Fox headed in their second and, although Tomlin's goal inspired a strong finish from Cardiff, Burton held on.
Cardiff City manager Neil Warnock said: "I'm disappointed but not heartbroken.
"It's a blessing that we've not picked up any injuries.
"At 1-0 I though about Mendez and Loic and at 2-0 I didn't want to put them on. Then we scored. But we had enough chances didn't we?
"I can't blame the ref for either of the goals but I think it was his first game at this level and I thought he was poor. It's a good job it wasn't a league match.
Burton Albion boss Nigel Clough said: "I thought it was a very good performance. The only thing we're disappointed with is we ended up hanging on at the end.
"The chances we had, we should have been maybe three goals ahead and then it wouldn't have mattered.
"It's a completely different team. Cardiff have rested 10 players and rightly so, when you're top of the league. I'm afraid that's of far greater importance than the cup."
- 5Ecuele Manga
- 15HalfordSubstituted forDamourat 81'minutes
- 34CoxeBooked at 33mins
- 23KennedySubstituted forMendez-Laingat 77'minutes
- 30BogleSubstituted forPilkingtonat 74'minutes
- 31M Harris
- 9ScannellSubstituted forSordellat 62'minutes
- 22FoxSubstituted forMcFadzeanat 76'minutes
- 36IrvineBooked at 68mins
- 26SbarraSubstituted forMurphyat 90+1'minutes
- John Busby
- Shots on Target
Second Half ends, Cardiff City 1, Burton Albion 2.
Attempt missed. Loïc Damour (Cardiff City) right footed shot from outside the box is too high.
Attempt blocked. Danny Ward (Cardiff City) right footed shot from the centre of the box is blocked.
Loïc Damour (Cardiff City) wins a free kick in the attacking half.
Foul by Ben Turner (Burton Albion).
Substitution, Burton Albion. Luke Murphy replaces Joe Sbarra.
Foul by Loïc Damour (Cardiff City).
Joe Sbarra (Burton Albion) wins a free kick in the defensive half.
Loïc Damour (Cardiff City) wins a free kick in the defensive half.
Foul by Damien McCrory (Burton Albion).
Attempt missed. Stuart O'Keefe (Cardiff City) right footed shot from outside the box misses to the right.
Attempt missed. Stuart O'Keefe (Cardiff City) left footed shot from the centre of the box is close, but misses to the left.
Corner, Cardiff City. Conceded by Tom Naylor.
Lee Tomlin (Cardiff City) wins a free kick in the attacking half.
Foul by Tom Flanagan (Burton Albion).
Attempt blocked. Anthony Pilkington (Cardiff City) header from the centre of the box is blocked.
Corner, Cardiff City. Conceded by Ben Turner.
Substitution, Cardiff City. Loïc Damour replaces Greg Halford.
Foul by Bruno Ecuele Manga (Cardiff City).