Dumbarton played some fine, passing football during the opening half hour and were rewarded when Dobbie netted from the spot after he had been felled inside the box by John Adam.
But the loss of the goal brought the visitors to life and Scott Michie should have done better than fire straight at Stephen Grindlay from six yards after good work by Andy Rodgers. Ex-Son Rodgers then fired across goal from a tight angle when a couple of his team-mates were unmarked in front of an empty net.
Neither side created a clear opening during and end-to-end second period until substitute Chris Hamilton found himself clear on goal with ten minutes to go only to be denied by the legs of Montrose 'keeper Andy Reid. The Sons eventually killed of their visitors' challenge when Craig Winter swung a corner to the far post and David Craig nodded the ball down for Dobbie to fire home from close range.