Tony Smith’s side showed tremendous work-rate, defending their line admirably for large periods against the Super League champions.
However, they were made to pay for a slow start when Saints cruised into a 10-0 lead inside just eight minutes.
Once Rovers lost a second forward to a HIA, Matty Storton joining Korbin Sims on the sidelines, Rovers were left with a lightweight, makeshift pack that, at one point, included two hookers and three back-rows.
With that in mind, they did well to limit the damage as much as they did when Saints predictably poured forward after the break.
Sims was wearing ‘Masoe 10’ on his shirt in honour of Mase Masoe, the club’s former captain who was at the stadium in St Helens as a guest of Sky Sports as part of this Super League round dedicated to him following his life-changing spinal injury.
But Sims, the Fiji prop signed from St George Illawarra this term, was helped off in the 20th minute after a shuddering hit from Alex Walmsley and never returned.
Late on, not long after on-loan Leeds Rhinos prop Muizz Mustapha came on for his Rovers debut, a third forward - impressive vice-captain Elliot Minchella - had to be helped off with a suspected ACL injury to add to their misery.
For Saints, Regan Grace showed remarkable footwork to score from Jonny Lomax’s arrowed pass in the corner for their opener and Jack Welsby quickly added a second try.
Given the pace with which Saints started, it would have been easier for them to concede again in a blistering start.
They managed to steady themselves, though, and recovered sufficiently to not only ensure there was no further score conceded before the break but make their own mark on the contest, too.
Jordan Abdull’s towering kicks pinned Saints back at times and a well-placed grubber from the stand-off also saw them force a drop-out.
Although they were unable to muster any points, with Shaun Kenny-Dowall offering a threat wide left and Jez Litten energetic in the middle, KR still had a shot trailing 10-0 at half-time.
Saints, though, turned the screw at the start of the second period, forcing two goalliine drop-outs before Tommy Makinson added a penalty.
Resilient KR managed to hold up Kyle Amor and Aaron Smith, Theo Fages kicking a drop-goal as a show of just how dogged the visiting defence was.
But Smith burrowed over once Lawler was off and Grace’s second made sure.
Hull KR: Quinlan; Crooks, Minkin, Kenny-Dowall, Hall; Lewis, Abdull; Sims, Litten, King, Linnett, King, Hadley, Lawler. Substitutes: Parcell, Minchella, Storton, Mustapha.
St Helens: Welsby; Makinson, Naiqama, Simm, Grace; Lomax, Fages; Walmsley, Roby, Lees, Thompson, Bentley, Mata’utia. Substitutes: McCarthy-Scarsbrook, Amor, Smith, Batchelor.
Referee: Robert Hicks (Oldham)