The Rams had one man sent off and three sin-binned while the Eagles had one player red carded and one sin-binned in an ill-contested fixture.
Dewsbury conceded eight penalties in the first half and lost Samy Kibula to a red card in an ill-disciplined and error-strewn first 40.
The Eagles were reduced to 12 men with 20 minutes gone as Bradley Tagg was dismissed for punching.
And two tries in the last five minutes handed the Eagles victory after the Rams had led for the majority of the contest.
After an even start, Dewsbury edged ahead through Paul Sykes' penalty goal.
Former Dewsbury Rams and Batley Bulldogs man Joel Farrell was then yellow carded for his involvement in an on-field melee.
The Rams almost crossed on the very next set but Rob Worrincy was held up in the corner.
The game became 12 against 11 when Tagg was sent off while Chris Annakin was sin-binned.
Farrell received a hostile reception on his return to Crown Flatt and got hit dangerously by Kibula who subsequently received his marching orders.
The Rams finally found some rhythm early in the second half and scored the game's first try following some brilliant work from Owen Trout.
On-loan Leeds Rhinos man Trout got on the end of his own grubber kick before offloading to Sykes who dove over next to the posts.
The hosts tightened their grip on the contest minutes later as Rob Worrincy squeezed over in the corner, just managing to stay in the field of play to get the ball down.
Sheffield had only lost one game prior to their clash with Dewsbury and weren't going away quietly, however.
After mounting some pressure on the Rams defence, Anthony Thackeray stepped through the line to dot down in behind the posts.
With just six points between the sides, Sykes kicked a drop-goal as the clock ticked past the hour mark.
Farrell copped another tough shot as Adam Ryder caught the second-rower with a high tackle. The Rams centre was shown a yellow card for the offence.
Jamaica international Farrell broke the line but was met by three Rams defenders who forced the knock on, much to the delight of the home faithful.
Liam Finn became the fourth player to be yellow carded as he made a superb try-saving tackle on Ryan Millar but was then penalised for holding down.
Farrell forced his way over on the next set, with Walker's conversion reducing the deficit to one point.
And things got worse for the Rams moments later as Ben Blackmore grounded in the corner, despite the Rams' appeals that the pass to the winger had gone forward.
Sheffield missed a late shot at goal as they held on in the closing seconds to hand Dewsbury their fourth defeat of the season.
Dewsbury Rams: Gabriel, Worrincy, Trout, Ryder, Brown, Sykes, Finn, Annakin, Day, Harrison, Knowles, Kibula, Trout. Subs: King, Mustapha, Mackay, Andrade.
Sheffield Eagles: Guzdek, Millar, Glover, Crookes, Blackmore, Walker, Thackeray, James, Davey, Dixon, Farrell, Davies, Brown. Subs: Burns, Broadbent, Makelim, Tagg.
Referee: Jack Smith.