The sheer enthusiasm of the Oldham side, playing in exile in neighbouring Rochdale a little over a year after re-forming following the demise of the former Oldham Bears Super League club, proved decisive.
Jason Clegg and the captain, Leo Casey, a popular choice as man of the match, were outstanding and typified Oldham's commitment, while Daniel Brown, the Australian half-back, matched a high work-rate with some much needed creativity.
Despite the tireless efforts of Barry Eaton at scrum-half and occasional moments of class from the former Bradford players Paul Medley and Nathan Graham, Dewsbury were forced into numerous handling errors and failed to capitalise on long spells of sustained pressure.
Deft handling by Damian Ball, Dewsbury's loose forward, created an early converted try for Billy Kershaw before Oldham turned the game on its head with three tries in an inspired seven-minute spell.
Emerson Jackman slipped out a superb pass for the winger Adie Mead to score midway through the first half and Brown linked with Graeme Shaw for the supporting Clegg to score. The French full-back Laurent Minut converted both tries. Then Brown, shaping to pass, fooled the Dewsbury defence and scythed over in the corner.
Brendan Williams, Dewsbury's Australian centre, reduced the arrears to six points at the interval with a powerful burst to the line. Oldham lost Minut, who twisted an ankle, at the start of the second half, but held on as Dewsbury pressed with increasing desperation. Brown, their stand- in kicker, then gave Oldham an eight-point cushion with a penalty.
William and Adrian Flynn almost scored a try for the visitors whose last hopes were extinguished when Casey hauled down Eaton inches short of the line.
Oldham: Minut; Mead, Leuila, Bostock, McNicholas; Jackman, Brown; Casey, Hough, Clegg, Shaw, Perrett, Martindale. Substitutes used: Coulter, Prescott, Quinlan, Peralta.
Dewsbury: Graham; Godfrey, Williams, Evans, Flynn; Agar, Eaton; Boothroyd, Delaney, Rose, Medley, Kershaw, Ball. Substitutes used: Firth, Haigh, Hicks, Long.
Referee: P Gilmour (Workington).