Kelepi Tanginoa popped up a one-handed pass for Broadbent to give Rovers the ideal start with the game’s first try from close range after just six minutes.
Talismanic prop Alex Walmsley endured a frustrating and blood-stained 300th appearance for St Helens.
He was having his head bandaged moments before Hiku stormed in for Rovers’ second try of the night, and then minutes later the former England and Great Britain international was held up over the line after taking a number of defenders with him as he attempted to touch down.
St Helens response, however, was only delayed by seconds as Jonny Lomax linked up with Murphy, who bounced over the whitewash to finish.
The visitors then had Dean Cross sin-binned for a high tackle on Arthur Mourgue, but they were back to full strength when Broadbent got on the end of neatly threaded kick from Jez Litten to grab his second try.
Lewis quickly followed that up with a dashing effort before the England half-back kicked and collected to set Minchella up for the host’s fifth score just before half-time.
It was a clinical way to finish the first 40 minutes against St Helens side that also lost full-back Jack Welsby to an apparent knee injury.
After the break, Murphy went for an audacious diving finish in an attempt to reduce the margin, but he failed to land his finish and was also injured in the process.
And it only got worse, with Lewis zipping over with a dummy and fend off to complete the win and add to his phenomenal scoring form against Saints – with the try his eighth in his past six games against them.