Morton preserved their unbeaten start to the season but only just as it took a dramatic late equaliser by full-back Peter Weatherson to give the nine-man visitors a point they thoroughly merited.
An entertaining and evenly-contested game appeared to be heading for an undeserved goal-less scoreline when, five minutes from time, the match suddenly erupted into a dramatic finale.
Sons' substitute Iain Russell started it all of with a darting run into the box where he was hauled down by Dean Keenan. Booked earlier, Keenan received his second yellow card before Russell kept his cool to sweep the spot-kick past David McGurn.
Morton stormed back, and a frantic scramble inside the Dumbarton penalty area saw Derek Lilley's effort somehow blocked on the line and put behind for a corner. The visitors continued to argue the the ball had crossed the line with the experienced Andy McLaren taking his comments too far, resulting in a red card from the impressive referee Mr Fyfe.
The drama, however, didn't end there. From the corner the ball was cleared only as far as Weatherson and he fired a low volley just inside Stephen Grindlay's left-hand post.
Earlier it had been the 'Ton who had come closest with Jason Walker twice having efforts cleared off the line, but the clearest chances fell to the home side, although neither Andy Rodgers or Craig Brittain could beat McGurn after being put clear through on goal.