On-fire Hull KR made it three wins in three meetings against St Helens this season to climb above cross-city rivals Hull into sixth place in the Super League standings.
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St Helens, who would have leapfrogged Rovers with victory, trailed 16-0 at half-time and could have no complaints at their first home defeat by the Robins since 2009.
Rovers, who had Travis Burns and Mickey Paea sin-binned by referee Robert Hicks, outscored their opponents three tries to two with Michael Dobson booting six goals from seven attempts.
Saints, who had lost twice at Rovers in the league and cup this year, brought back Stuart Howarth for Luke Thompson but Ade Gardner was still missing as his wait to score the one try he needs for a career double century of touchdowns goes on.
Rovers were without Matt Salter, Rhys Lovegrove and Sean Gleeson after the impressive win at Catalan with Alex Brown stepping onto the wing and Aaron Ollett making his Super League debut off the bench.
Richard Beaumont was a late replacement on the bench after Lovegrove was taken ill before the match.
Lincoln Withers and Jason Netherton were still absent for Rovers whose only defeat in their last six matches was the controversial Magic Weekend loss to Hull.
Saints had won the last four home meetings against the Robins since 2009 and went into the clash on the back of impressive victories over Bradford and Salford.
Hull KR stunned their hosts by taking an eighth minute lead with a Travis Burns try after the Australian stand-off scythed through the defence and Newcastle Knights-bound Dobson slotted over the conversion.
Then almost straight from the restart Burns burst through again with Greg Eden kicking ahead for Brown to shrug off Francis Meli and go over in the corner to open up a 10-0 lead.
But Rovers had to manage without Burns for 10 minutes midway through the first half after he was sin-binned with Paul Wellens after a flare-up.
Wellens was furious with the decision and Saints' plight became worse when Eden scooped up a pass from Dobson to make it 16-0.
James Roby failed to find touch from a penalty just before the break to sum up the home side's frustrations.
St Helens continued to make mistakes early in the second half but finally opened their account after 49 minutes when Meli took Jonny Lomax's pass to cross in the corner and Gareth O'Brien landed the touchline conversion.
A Dobson penalty eased Rovers nerves to make it 18-6 after 55 minutes when Saints threatened a comeback.
Rovers had Paea, who this week agreed to join Hull next season, sin-binned on the hour for a professional foul but two more Dobson penalties stretched the advantage to 22-6.
Anthony Laffranchi did manage a converted touchdown for Saints six minutes from time but it was too late with Dobson adding another penalty.