Rams trailed 24-0 at half-time and didn’t improve after the break as the visitors had three players sin-binned and were unable to prevent Oldham running in seven tries.
Oldham raced into a sixth-minute lead when centre Tom Ashton broke through and raced over wide on the left.
Dewsbury’s display was littered by handling errors and dropped ball but they were not helped by a hefty penalty count against them.
Dale Morton had a try ruled out for off-side before Oldham grabbed a second try when they were marched downfield by three consecutive penalties and Gareth Owen danced between the posts, with Lewis Palfrey converting. Dalton Grant was sin-binned for an alleged trip and on the back of the penalty, Danny Langtree raced over wide out with Palfrey converting then tagging on a penalty.
Langtree intercepted a wayward pass and stormed between the posts for Oldham’s fourth try, which Palfrey improved. Dewsbury’s Ryan Wright charged down a kick-through but as Joel Farrell appeared certain to score, he was pulled back by Richard Lepori.
Referee Joe Cobb chose to only sin-bin the Oldham full-back instead of showing a red card.
At the start of the second half Dalton Grant pounced when Oldham knocked on Reynolds’ up and under. Reynolds converted. Oldham responded with a Michael Ward try at the side of the posts, which Palfrey converted, stretching his side’s lead to 30-6. Grant was on the end of a sweeping move to grab his second try before Dewsbury hopes were ended in just 60 seconds.
Nathan Conroy was sin-binned and on the back of a penalty Owen crashed over for his second try. As the Rams lined up for Palfrey’s conversion, Reynolds was sin-binned for speaking out of turn and Dewsbury were down to 11 men.
Adam Clay grabbed Oldham’s seventh try four minutes from time before Jack Teanby grabbed a consolation Rams try which Paul Sykes converted.
Oldham: Lepori; Clay, Ashton, Bibby, Holmes; Palfrey, Grimshaw; Joy, Owen, Spencer, Langtree, Hope, Thompson. Subs: Gee, Ward, Hughes, Crowley.
Dewsbury: Guzdek; Morton, Sykes, Crookes, Grant; Reynolds, Kain; Groat, Conroy, T Adamson, Trout, Grady, L Adamson. Subs: Wright, Teanby, Tinks, Farrell.
Referee: Joe Cobb.