Goals by Derek Lilley and Peter Weatherston gave Morton the points which keeps them in the promotion hunt, but this reversal - the third straight home defeat - leaves the sorry Sons struggling at the other end of the table.
Iain Russell gave the home fans an early boost as his first-minute shot forced the visiting 'keeper into a low save to his right, but it was his opposite number Stephen Grindlay who kept the score-line blank with outstanding saves from Scott McLaughlin and Lilley within the first 12 minutes.
It was all Morton, and the opener duly arrived mid-way through the half. Chris Millar sent over a hanging cross from the right, and Lilley got above everyone at the back post to send his header across and beyond Grindlay.
The clincher came just after the re-start when Andy McLaren's near-post corner was flicked across goal by the head of Dumbarton's John Gemmell and unfortunately for the big striker straight into the path of Weatherston, who buried the ball in the net with a fierce low drive.
Dumbarton battled away but were totally without threat up front. They almost grabbed a consolation deep into injury time courtesy of a splendid 25-yard free-kick by substitute John Dillon, but his effort crashed back off the underside of the bar with Stefan Gonet well beaten.