Saints had struggled for cutting edge as they drew their first three games in the competition - requiring penalties on each occasion to claim the bonus point.
But Cammy Smith grabbed a double, with Haydon Coulson, Ross Stewart, Stephen McGinn and Jim Kellerman also netting as the Buddies sliced their Ladbrokes League One opponents to ribbons while handing new boss Alan Stubbs his first victory since replacing Jack Ross.
It took just two minutes for Coulson to carve his way through the Sons as he drove in from the left, nudged the ball beyond Ross Perry before racing on to slam past Grant Adam.
Coulson smashed the frame of the goal after another impressive foray forward but the second strike came 10 minutes before the break as Paul McGinn collected Danny Mullen’s ball out wide before swinging a cross deep to the back post, which Smith nodded back across Adam and into the corner of the net.
And McGinn was involved again three minutes after the break as the match was put to bed. With a cross-field pass, Cole Kpekawa found the right-back who then drove to the by-line after a quick exchange with Danny Mullen and his cross wriggled its way to the back post for Stewart to head home.
Skipper McGinn then lashed a sensational 25-yarder home on 53 minutes before substitute Kellerman grabbed the fifth eight minutes from time as he bundled home from close range.
And Smith saved the best to last as moments later he lobbed Adam from 40 yards out.