League One City, who were 2-0 down after 38 minutes, claimed the biggest scalp of their recent giant-killing exploits to advance to the fifth round and end Chelsea’s hopes of challenging for an unprecedented quadruple.
Chelsea reject Filipe Morais levelled the fourth-round tie with 15 minutes to go before Jon Stead, the scorer of City’s first, teed up Andy Halliday for the winner eight minutes from time.
And substitute Mark Yeates tucked in a stoppage-time fourth to inflict the Blues’ first home loss this season and spark jubilant celebrations from Phil Parkinson’s visitors.
Chelsea boss Jose Mourinho said it would be a “disgrace” if his side exited the competition to the League One Bantams, who beat Arsenal and Aston Villa en route to the 2013 League Cup final, where they were beaten by Swansea.
But Mourinho’s men were distinctly second best and not even the introduction of Cesc Fabregas, Eden Hazard and Willian off the substitutes’ bench could rescue the tie.
It was the first time Chelsea have lost to lower-league opposition at home since 1995 against Millwall.
Chelsea made nine changes with Tuesday’s Capital One Cup semi-final second leg against Liverpool in mind, but still fielded a team full of talent worth an estimated £98million. The fees for Bradford’s starting XI totalled £7,500.
The Blues must now regroup for their midweek clash with the Reds and next Saturday’s Premier League showdown with Manchester City.