In appalling conditions that deteriorated as the error-strewn contest went on, a much changed home side led 12-0 at the break and 14-0 inside the last 10 minutes before the Hawks scored a late consolation.
For Fax the end justified the means, with a place in the next round never really looking at risk against James Coyle’s team.
Halifax had a scoring chance inside two minutes, makeshift winger Chester Butler being shovelled into touch as he made for the corner.
But having not taken that opportunity, they did take their next, back rower Ed Barber driving hard for the line.
Halifax added to their tally on 25 minutes, Gareth Moore’s kick claimed by Butler for the try.
Steve Tyrer was on target from the sideline and the centre stretched the home side’s lead to 12-0 with a 50-metre penalty.
The second half was equally unspectacular, although Hunslet did produce their first real moment of attacking threat when Joe Sanderson sent Liam Mackay through, only for the cover to converge a metre from the line.
Tyrer tapped over a second penalty for a 14-0 lead but Hunslet finally scored with eight minutes to go through winger Ryan Ince, Daniel Ansell converting. Fax replied, Rob Worrincy touching down in the corner and Tyrer adding the goal.
Halifax: Sharp; Butler, Tyrer, Woodburn-Hall, Worrincy; Johnston, Moore; Tangata, Kaye, Cahalane, Grady, Barber, Morris. Substitutes: Nelmes, Ambler, Mammone, Cullimore
Hunslet: Watson; Ince, Wilson, Mvududu, Webb; Gibson, Ansell; Hesketh, Lee, Carbutt, Walton, Normington, Mackay. Substitutes: Flanagan, Sanderson, Flynn, Kenga
Referee: T. Grant (RFL).