Relegated Blackburn picked up their their first points of the League One season and inflicted Bradford's first defeat with a hard-earned 1-0 win at Valley Parade.
The winning goal came in the 47th minute when winger Craig Conway delivered a testing cross from the left and striker Dominic Samuel stooped to head the ball into the bottom corner of the net from just inside the six yard box.
Up to that point, Bradford's Republic of Ireland keeper Colin Doyle had rarely been tested in a scrappy first half of few clear cut chances at either end.
Bradford, who did not lose a single league match at home last season on their way to the play-off final where they were beaten by Millwall, had begun the new campaign with two wins.
However, they made little impression on a strong Blackburn defence despite making a triple substitution in the 68th minute, which included bringing on last season's main strike force, Charlie Wyke - for his first appearance of the season after recovering from a hamstring injury - and Alex Jones.
David Raya in the Blackburn goal had few direct shots to save.