They had keeper Jamie Langfield to thank, however, for the fine save he made from St Mirren's in-form striker Esmael Goncalves in the dying stages, with the game teetering towards the Saints.
The Dons went into the game without a win in their last five games but made just one change to the side defeated by Hibs in the Scottish Cup last Sunday, with Peter Pawlett starting in place of the benched Rob Milson.
At the other end, Steven Thompson's knockdown allowed Gary Teale the chance to shoot from 20 yards, but the former Scotland winger sliced his effort well wide of Langfield's post.
The game had failed to spark into life on a pitch that had clearly suffered for hosting Scotland's international victory over Estonia in midweek, but there was the glimmer of an opportunity when the Dons' Reynolds hauled back Goncalves, earning the game's first booking.
Teale lined up the free-kick, 22 yards out and to the left of centre, but blasted his shot straight at the wall.
Moments later Reynolds was joined in the book by St Mirren's Kenny McLean, but the Dons' set-piece also came to nothing.
St Mirren's biggest threat throughout the first half had been the runs of Paul Dummett from left-back and, just before half-time, he put in a low cross which required the intervention of Reynolds and Joe Shaughnessy to turn it behind for a corner.
Langfield had to be on his toes early in the second half to palm Teale's powerful angled drive over the bar and 10 minutes after the break, the goalkeeper was called upon to mop up Paul McGowan's weak header from a left-wing cross.
St Mirren were finding their way into the game, though, and on the hour mark McLean saw a thunderous drive blocked by Langfield, before Pawlett blocked his follow-up effort.
Isaac Osbourne became the third man to go into the book when he caught Conor Newton with a trailing leg after 64 minutes.
And then came the substitutes, first Josh Magennis and then Scott Vernon, with Clark Robertson and Stephen Hughes the men replaced.
But after 73 minutes, all hell broke loose. Reynolds lifted an arm as he charged to block a McLean shot, with Beaton ruling it had been a deliberate handball.
The Dons man received a second yellow card, and the Saints had a free-kick just a yard or so outside the area, but ultimately McLean's shot was wasted.
St Mirren had the best chance of the match as the game entered a frantic final five minutes when McGowan worked the ball across the face of goal to the unmarked Goncalves, but Langfield was alert to the danger and spread himself to block as the striker tried to lift the ball over him.