Richard Marshall’s part-timers had defeated the Championship leaders in their final regular-season game a fortnight earlier but were given little hope of repeating the feat in this Qualifiers opener away at Craven Park.
Nevertheless, they gave Rovers – desperate to make an immediate return to Super League – an almighty scare in a thrilling contest.
Leading 16-14 at the interval, the West Yorkshire side extended their lead with winger Heaton’s fourth try in the 52nd minute and, despite the erratic hosts replying via George Lawler just after the hour, seemed ready to hold on for a famous win.
However, despite a truly heroic defensive effort, including four consecutive sets on their own line, they finally broke when former Bradford Bulls prop Scruton crashed over eight minutes from time, the under-pressure Robins avoiding a catastrophic third successive loss.
Relieved KR were thankful to Shaun Lunt, their dynamic former England hooker who kept driving them forward despite their scrappy play; without him, they would surely have endured the worst possible start to their promotion bid.
Yet, initially, it all looked so simple for the hosts; Rovers took just 41 seconds to get off the mark when they won a short kick-off and Lunt fed Kieren Moss, who sliced over from close range.
The full-back was in again soon after when Halifax prop Ryan Boyle made a complete mess of Jamie Ellis’ angled grubber.
Ellis, though, struck a post with both conversion attempts so they were only 8-0 in front.
That meant, when Heaton surged in for his first in the 10th minute, the first of Steve Tyrer’s three conversions meant they were quickly back in touch.
Matty Marsh threw a dummy to arc over from 15m as a rogue Halifax defender shot out of the line, Ellis finally adding a goal, but Rovers then began making unforced errors.
Moss coughed up a pass as did Marsh before even Lunt, unusually, produced a forward pass to waste another attacking opportunity.
From that latest mistake, Halifax capitalised, second-row Mitch Cahalane showing deft hands to unleash Barber, the excellent centre providing the final pass again for Heaton’s second.
Next, when Mose Masoe – the giant former St Helens prop on debut for KR after moving from St George Illawarra – spilled on the second tackle on his own 20m line, the winger was in for his treble with just 26 minutes gone.
Will Sharp, initially, looked to have blown an overlap chance which left the waiting Barber fuming.
However, at the next play close to Rovers’ line, Barber did receive possession and duly produced a wonderful swift pass to supply his winger yet again. There was no conversion but Fax led 16-14 and Tim Sheens had clearly seen enough.
As the sides waited to kick-off, the KR coach very publicly switched his centres over, the troubled Thomas Minns moving to the right with Andrew Heffernan taking his place to try and snuffle out Barber’s obvious threat.
Still, Simon Grix broke through the middle as Fax continued to cause problems, KR’s problems highlighted as Ellis skewed a kick straight into touch.
Minns was replaced at the break but their issues carried on as Justin Carney botched Scott Murrell’s grubber and Barber stabbed on the loose ball for Heaton to add his fourth.
The 27-year-old had only scored five tries beforehand all season.
Sheens’ promotion-hopefuls side finally found some rhythm, though, mainly down to Lunt’s probings and a decent second spell from Masoe to break Halifax hearts and end their four-match winning run.
Hull KR: Moss; Shaw, Heffernan, Minns, Carney; Marsh, Ellis; Scruton, Lunt, Jewitt, Blair, Addy, Kavanagh. Substitutes: Masoe, Lawler, Mulhern, Atkin.
Halifax: Sharp; Heaton, Barber, Tyrer, Worrincy; Murrell, Johnston; Mammone, Moore, Boyle, Grady, Cahalane, Grix. Substitutes: Kaye, Morris, Sio, Douglas.
Referee: Liam Moore.