Alan Maybury's men are in pole position to progress ahead of Saturday's return leg as an Ouzy See brace, John Robertson strike and own goal from Sons defender Gregor Buchanan, rounded off a remarkable night at Ainslie Park. Not even a Ross MacLean header could put a dampener on things.
However, Maybury has urged his players not to become complacent and insists they will be going to the Rock in hope of killing the tie
"I want to go and win the game on Saturday so that's my attitude," said Maybury, who has done his chances of landing the job on a permanent basis no harm. "Last weekend's loss at Stirling didn't sit comfortably with me having to manage the game ahead of this one. I didn't want to give up the momentum we've been on. So, we'll be going to Dumbarton to win. If we have to sit in and defend then so be it.
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"Listen we spoke before the game about making sure we are still in tie come Saturday, whether we won or lost. There has been a couple of times this season we have given away sloppy goals so it was important we managed the game as it is over two legs.
"We got gifted the first goal and then we managed to really work our way into the game and create chances. Even when they got a goal back, I would have taken 2-1, maybe even 2-2 but it opened up a little bit near the end and we scored two good goals.
"It gives us a good advantage but we have to temper that. It's a step forward but we've got to go and do it all again on Saturday. We're delighted with the result but we're certainly not getting carried away."
It was the Sons who were fast out of the traps as they had two attempts on goal inside the opening three minutes, Joshua Oyinsan coming within inches as his header just evaded the top corner. But Stevie Farrell's side gifted the hosts the opener when George Stanger misjudged his passback and See nipped in ahead of the onrushing Kieran Wright, took one touch to round the goalkeeper, and shot into the empty net.
Ryan Shanley spurned a golden opportunity to double the home side's lead as he glanced a header wide from a sumptuous Cammy Logan cross. Oyinsan was guilty of passing up a similar chance just 60 seconds later before the visitors' defensive frailties reared their ugly head once more.
Danny Handling's corner was pinged into the centre of a packed six-yard box and it ricocheted off the standing leg of the unfortunate Buchanan and past his team-mate.
City continued to pepper the Sons goal with Handling and Innes Murray both going close. However, Dumbarton had City camped in their own half after the interval and they got their rewards on the hour when Paul Paton picked out MacLean, whose looping header landed just under Brian Schwake's crossbar.
It was now very much backs to the wall stuff as the Sons hunted down an equaliser, but they had the stuffing knocked out of them when See found the bottom corner with a crisp effort to restore City's two-goal advantage with just under 20 minutes remaining.
And City were in dreamland in stoppage time when more hesitancy in the Sons rearguard allowed substitute Robertson to add a fourth.