Deane Smalley's first-half strike gave title-chasing Chesterfield a 1-0 victory and increased the pressure on Bradford manager Peter Taylor.
After six games without a win, John Sheridan's men have now registered successive victories over Lincoln and Bradford to issue a timely warning to the chasing pack.
Smalley, on loan from Oldham, marked his return from suspension by giving the leaders a 16th minute advantage which they held despite late pressure from the Bantams.
Running on to Kieran Djilali's defence-splitting pass, Smalley wasted no time in pulling the trigger from just inside the penalty box.
Chesterfield should have doubled their advantage when the unmarked Djilali volleyed straight at Bradford keeper Lenny Pidgeley in the 38th minute.
Bradford improved after the break as substitute Jake Speight livened up their attack and Tom Adeyemi having a header well saved by Tommy Lee, but Chesterfield's defence stood firm with Dean Holden and Ian Breckin outstanding.
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