Nelson cruelly missed out on a place in the Lancashire League’s top flight after being bowled out for 49 on the final day of the season.
Russell Bradley’s side went into the game at Rochdale equal 10th in the table, eight points clear of 13th place Todmorden.
But after Rochdale captain Michael Harling won the toss and chose to field, he took 4-11 as the visitors were dismissed within26.4 overs for less than 50.
Opener David Crotty made 20 of those – to finish with an impressive 658 runs for the season – before being seventh man out at 39, and only Caleb Grant (10) could join him in double figures, with 10 extras bumping up the total.
Rochdale sub professional Sean Ervine took 3-5 and Steve Oddy 2-26.
Ervine then hit an unbeaten 26 to secure Rochdale’s place in the top division with a six-wicket win inside 14 overs.
Sub professional Ashar Zaidi took 3-19 for Nelson, who will now play their cricket in the second tier next year.
They will be joined by derby rivals Colne, who signed off with a seven-wicket win at Great Harwood.
Matt Walker won the tss and inserted the hosts, and John Lambert took 3-23 and Walton 3-55 as Great Harwood were all out for 149.
Harwood professional Ashen Silva top-scored with an unbeaten 43 after openers Allan Armer (21) and Matthew Oddie (22) had shared 43 for the first wicket.
Colne’s target was reduced to 144 by rain, and Chris Walton hit 64 not out to steer them home with three wickets down.
Walton’s innings contained 11 fours, as he put on 94 for the third wicket with Kenton Rhodes, who made 45.
Stuart Maher took 2-22 for the hosts, removing professional James Price for a duck, and Adam Procter for 3.
Meanwhile, in the Ribblesdale League, Barnoldswick’s fate was sealed by the inclement weather.
Barnoldswick went into the final game nine points adrift of safety after a see-saw penultimate weekend.
Their task looked ominous as they were due to host champions Oswaldtwistle Immanuel, but no play was possible, meaning Jonathan Beech’s side are demoted to Section B.
Earby’s game at home to promotion hopefuls Ribblesdale Wanderers also fell by the wayside, as they closed the season next bottom.