The hosts led 18-0 at half time and despite a spirted fightback, the visitors had left themselves with too much to do to overturn the deficit.
The Rams had been bolstered by the loan arrivals of Riley Dean, Robson Stevens and Jimmy Beckett but were left without a win in five against in-form 'Haven, who have now won their last four fixtures in Cumbria.
The Cumbrian side are just one place outside the play-offs while Dewsbury are teetering dangerously above the relegation zone.
Louis Jouffret gave the home side the lead after 15 minutes before Nikau Williams added a converted try eight minutes later.
It only took a minute for a third Haven try to arrive as Andrew Bulman dotted down before the same man scored the hosts' fourth try of the afternoon six minutes before the interval.
Just before the hour, Andy Gabriel sparked Dewsbury into life before Jordan Schofield reduced the deficit to six points with a second try five minutes later.
The decisive moment came on 66 minutes when Whitehaven increased their advantage to eight points with a penalty goal.
With six minutes remaining, Davey Dixon restored hope for the visitors as he crossed for a third Dewsbury try but that was as close as Lee Greenwood's side got as the hosts held on to inflict a fourth-straight defeat on the Rams.