Luke Oliver scored a late winner as struggling Bradford stunned Southend United, who squandered the chance to go top of League Two.
The centre-back scrambled the ball home from close range following Andrew Davies's pass in the 88th minute.
City deserved the win and Michael Flynn's free-kick forced a save from Luke Daniels in the first half.
Southend offered little going forward, although John McLaughlin did save Anthony Grant and Liam Dickinson shots.
The result caps off a poor week for the Shrimpers, who lost 3-0 to Cheltenham on Saturday to drop from the top of the table and then lost to Oldham in the FA Cup on Tuesday.
Bradford's first league away win of the season lifts them up to six points clear of the relegation zone.
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Southend United manager Paul Sturrock told BBC Essex:
"We've been going down the road recently with a lot of players jumping off treatment tables to play games on a Saturday with no training in the week.
"Three or four have been of that ilk and we've had players suspended coming back.
"Players have flu and that kind of thing so it's a culmination of a lot of things. And having to play Tuesday and Friday we never legislated for that and I think we paid dear."