A much-changed side never looked convincing against their neighbours, but Knox's opportunism was just enough to keep their noses in front.
Paul Anderson, a recent Bulls signing from Halifax who joined the club too late to qualify for Wembley, showed his potential with some storming early runs. From one of the first, he got away a clever pass to send Knox in for the game's opening try, converted by Steve McNamara.
When Halifax drew level after 13 minutes it was as the result of a suspiciously forward pass from Wayne Jackson that released Damian Munro.
Both sides looked badly disorganised until Bradford again opened up Halifax for Matt Calland to put them back into the lead. Martin Pearson missed a penalty for Halifax, but more than made up for that with a scooting run down the wing for his side's second try.
Bradford, with a number of first-team regulars missing, were looking vulnerable, but they held on to a narrow advantage in a scrappy game until half-time.
Soon after the break, they produced their best handling of the match so far for Knox to claim his second try. Even then, Halifax should have replied almost immediately, Paul Rowley supporting Mike Umaga's run but losing the ball as he dived over.
They were not kept out for long. Paul Cook knocked on to concede a scrum and from it Martin Moana cut through and Pearson's boot levelled the scores.
The Bulls hit back when McNamara dived on to James Lowes's kick to touch down, adding the goal point himself. Another Lowes kick, this time re- gathered and passed on to give Knox his hat-trick and Bradford began to look comfortable for the first time.
That comfort was short-lived. Pearson showed great strength to go over and, four minutes later, Rowley's pass sent Chris Chester racing in. Pearson's kick brought Halifax to within two points, but despite pounding Bradford's line at the end, that was as close as they could get.
Bradford Bulls: Cook; Ekoku, Calland, Loughlin, Scales; Bradley, Tomlinson; Anderson, Lowes, Reihana, Knox, Dwyer, McNamara. Substitutes used: Wittenderg, Peacock, Graham.
Halifax Blue Sox: Umaga; Munro, Pearson, Moana, Amone; Chester, Parker; Harrison, Rowley, Skerrett, M Jackson, Gillespie, Baldwin. Substitutes used: Dean, Highton, Bouveng, W Jackson.
Referee: D Campbell (Widnes).
Halifax's prop forward Kelvin Skerrett was taken to hospital after the game suffering with a broken arm.Reuse content