Morley opened the scoring with a try from Dante Van De Merwe converted by Mark Chester.
Steve Nutt slotted a penalty for the visitors before Rossendale took the lead with a try from Danny Collins after the pack had exerted pressure on the Morley line.
Anthony Bingham added the second, a neat chip over the defence from Nutt creating the opportunity for the winger.
Jamie Albinson scored the third, backing up a break by Paddy Pole straight from the restart. Nutt slotted the conversion but Morley hit back just before the break with a try from Luke Watts for 12-20 at half time.
In the second half Ryan McKibbin brought up the bonus score, again off solid phase play from an attacking scrum.
Morley however were not done and narrowed the gap with a try from Tom Clough again converted by Chester but although Nutt eased tensions with a penalty, a second try by Clough, and the bonus point, converted by Chester made it a two point game with nerves set jangling for a second time.
In the final minutes an interception by Nutt set Bingham away to seal the win for the Lancashire side with Nutt's conversion denying Morley a second bonus point.
Geoff Lightfoot