The Rams had lost their previous two outings by heavy score-lines but responded well against struggling Oldham to claim their fourth win of the Championship campaign.
Dewsbury led 12-0 at the half-time interval and never looked in danger of losing their lead as Oldham managed to score just one try in 80 minutes.
The Rams scored twice in quick succession early on as Paul Sykes put Davey Dixon over for a try before Andy Gabriel showed a fantastic turn of pace to score his eighth try of the campaign on 13 minutes.
Sykes converted both tries as the Rams held their 12-point advantage until the break.
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Tyler Dupree hit back for Oldham with 56 minutes played but the missed conversion meant Lee Greenwood's side were able to keep their opponents at arm's length.
Dewsbury responded five minutes later as Will Oakes showed great strength to power through two defenders for a try which quickly quelled Oldham's hopes of mounting a comeback.