Without moving out of first gear, the champions had the points effectively sewn up within the opening 20 minutes.
Their opening goal was fashioned down the left by a combination of Gavin Skelton and John O'Neil whose deep cross was met at the back post by the unmarked Ryan McGuffie with a firm header.
Six minutes later a corner was missed by the entire home defence and Chris Innes swept the ball low into goal from 12 yards.
Thereafter Gretna were content to knock the ball about and, although they won a couple of corners at the start of the second half, Dumbarton never posed a threat to David Mathieson in the visiting goal.
Gretna introduced Dene Shields into the fray for the final quarter and he was only denied by a flying save by Stephen Grindlay who turned aside the forward's curling effort from 20 yards.
Shields then sent Steve Tosh clear in the box but he drove weakly into the side-netting.
The Sons eventually managed a shot on target in the dying seconds when Mathieson blocked with his legs from Andy Rodgers, but Dumbarton now face a vital trip to fellow strugglers Alloa in a game which will surely decide which side will drop into Division Three.