Rovers did enough in the first half to win the game; taking a 24-12 lead in at the half-time interval after tries from Makali Aizue, Jon Steel, Ben Cockayne and Ben Fisher along with four goals from Gareth Morton.
The Vikings had opened the scoring with a penalty goal from Mick Nanyn but quickly fell behind, tries from Damien Blanch and Daryl Cardiss along with a second goal from Gavin Dodd giving them their 12 points.
The Robins kicked two penalty goals after the break to extend the lead, but where kept try-less in the second half as a result of an improved Widnes performance.
Tries from Aaron Summers and Mark Smith brought the scoreline to 28-22 and the visitors were hopeful of drawing level; however Rovers held on until Scott Murrell’s last second drop goal sealed the game.
Widnes will now face Whitehaven on Sunday to decide who will go through to the final after the Cumbrian side eased past Batley Bulldogs 30-0 at the Recreation Ground.
Either Swinton or the Crusaders will face off with Sheffield Eagles in the play-off final to decide who will make the move up into National League One.