Lincolnshire ended day two of their Minor Counties Championship match at Barrow-in-Furness in a commanding position.
Having set Cumberland a target of 365, Jonathan Davies capitalised on the wicket he claimed at the close of day one, taking a second before the home side had added to their overnight score of 26.
And Bob Chapman quickly got in on the act with the wicket of Ashley Metcalfe to make it 33 for three.
Opener Oliver Clayson and number five Graeme Lloyd stopped the slide with a stand of 76. But when both fell to Dowman - Clayson lbw and Metcalfe to a diving catch at gully by David Christmas - the Cumberland innings crumbled from 120 for four to 154 all out, wicketkeeper Oliver Burford taking three catches and one stumping.
Dowman finished with three for 29 and Davies two for 30, both off 12 overs while Elliot Wilson took two for 37 off nine and Christmas followed up his excellent opening day innings with an economical two for 17 off 14 overs, eight of which were maidens.
Mark Fell then invited the home side to follow on and the second innings brought a steadier performance as Steve Knox made 29, Clayson 26, Metcalfe 34 and Lloyd 58 off 77 balls in which he hit 11 fours.
Jason Quint contributed 31 and at the close of play Cumberland were 244 for five, O'Shaughnessy unbeaten on 31 and Christmas adding two more wickets to his tally.
Cumberland go into the final day 33 ahead with five wickets standing, and Fell will be looking for early bowling success to leave Lincs an achievable target.