Halifax moved to within 80 minutes of the Championship Grand Final with a dominant 21-6 win at champions Sheffield.
Fax, who now get a week off before taking home advantage, produced a smothering defensive effort to run out convincing winners.
After a scoreless first half, Fax hit the front three minutes after the break when prop Andy Bracek gathered a Paul Handforth grubber kick and drove over the line, Steve Tyrer adding the conversion for a 6-0 lead.
Skipper Scott Murrell then had a try ruled out, Fax’s third of the night, before Tyrer’s 65th-minute penalty put Fax 8-0 up.
Murrell almost scored immediately after that, just fumbling his own kick on the try line.
But Craig Ashall added a drop goal to edge the score out to 9-0 as Sheffield’s attack became increasingly desperate.
They got some reward when Vinny Finegan scored after an awful error from Ryan Fieldhouse, Dominic Brambani making it 9-6 as the end of normal time approached.
But the visitors eased their nerves - and made sure they got exactly what they deserved - when Luke Adamson set up Paul Handforth for the winner before Murrell crossed in the final seconds, Tyrer converting both.
Fax had the better of a tense opening 40 minutes, with back rower Ross Divorty and replacement forward Luke Ambler both racking up the metres as the visitors rolled forward with real efficiency.
They forced referee Dave Merrick to go to the video referee twice; first when Divorty touched down after forcing an error from Alex Szostak and second when Ambler claimed a fleeting touch as the ball ricocheted in the in goal.
Neither try was awarded, while at the other end the Eagles always presented a threat with Menzie Yere and full back Quentin Laulu Togagae ever dangerous.
The home side were reduced to taking a penalty shot from inside their own half to try and break the deadlock just before half time, but Brambani put the ball wide as the sides went to the interval at 0-0.
Sheffield: Laulu Togagae; Finigan, Yere, Armstrong, Turner; Walker, Brambani; Battye, Henderson, Stringer, Knowles, Szostak, Hirst. Subs: Green, Davey, Higgins, Garside
Halifax: Fieldhouse; Sheriffe, Tyrer, Heaton, Reittie; Murrell, Handforth; Tonks, Ashall, Davies, Manning, Divorty, Adamson. Subs: Ambler, Bracek, Robinson, Holden
Referee: Dave Merrick