Third tier Burton are into the semi-final for the first time in their history after a shock 1-0 win at Championship promotion chasers Middlesbrough.
Sixth in the second tier, Middlesbrough made a host of changes and were punished by their lowly opponents.
Burton, 15th in League One, are the first team from the third tier or lower to reach the semi-finals since Sheffield United in 2014-15.
Jake Hesketh put Nigel Clough’s side into the lead in the 48th minute, the on-loan Southampton midfielder firing home from the edge of the area.
Clough won the League Cup twice as a player with Nottingham Forest in 1989 and 1990.