A second-half siege by the Wasps was finally rewarded with an injury-time equaliser by former Son Jordan Kirkpatrick, who rifled in an extra-time winner.
Victorious manager Jim Goodwin said: “The boys simply never gave up. Dumbarton are a very good side defensively but we kept on going until we found a way through. I am delighted that we are heading up a level.”
Kirkpatrick, who was available despite suffering a back spasm in midweek, could have levelled the tie after only 15 seconds. The striker was fed the ball by Ross Stewart, but Dumbarton goalkeeper Scott Gallacher produced an outstanding block from close range and Iain Flannigan tapped the rebound wide.
A misplaced pass by Kirkpatrick which went straight to Calum Gallagher gave Dumbarton their first chance in nine minutes but Gallagher’s speculative effort from 40 yards was tipped past the post by Neil Parry.
It looked like the hosts had taken a huge step to reaching safety four minutes from the break when David Smith picked out Kevin Nisbet at the back post and the striker’s header back across goal looked a goal all the way until Parry stuck out an arm and pushed the ball away.
Scott Taggart saw a low shot saved early in the second half and, as Alloa built pressure, Andy Dowie was only inches out from heading into his own net, and Stewart could only flick the ball into Gallacher’s arms following a corner.
The home goal led a charmed life with Alloa coming close to the goal they craved three times in the space of a minute with an hour played. First-half substitute Callum Smith looked to have scored with a header from a Taggart cross but Gallacher produced a fine save and Dowie blocked Stewart’s follow-up.
The ball was eventually cleared, but when it was played back Smith wriggled clear. However, his shot came off the outside of the post.
The one-way traffic continued and Callum Crane picked out Cawley with a cutback. However, the attacker dragged his shot wide and shortly afterwards Dowie threw his body in the way of shots buy Cawley and Kris Renton.
Alloa manager Jim Goodwin, who was listed as a substitute, was shown a yellow card with ten minutes to go as his frustrations at Dumbarton slowing the game down got the better of him.
Goodwin’s side kept on pushing and they drew level in the third minute of injury time when Stewart drilled in after a Renton pass. Then, Five minutes into added-on time Kirkpatrick shot high into the net after a free-kick had broken into his path.
Dumbarton manager Stephen Aitken said: “It looked like we had done enough. However, it was not to be. It is very disappointing to be leaving this level of football after six seasons.”