The Dons looked set to ease to their fourth victory of the season after taking an early 2-0 lead when Scott Vernon netted after only 40 seconds and Rory Fallon's diving header doubled their advantage after 17 minutes.
However, Kenny McLean latched onto a Steven Thompson header to pull a goal back 10 minutes before the break and Graham Carey's wonderful 35-yard free-kick after 52 minutes earned the Buddies a point.
Fraser Fyvie appeared to have scored a late winner for the Dons when his cross was fumbled into the net by Craig Samson, but the goal was ruled out for offside and the midfielder was shown a straight red for dissent following the decision.
Aberdeen boss Craig Brown, who took charge exactly a year ago, made two changes from last weekend's 2-0 defeat to Kilmarnock with Icelandic international Kari Arnason and youngster Ryan Jack returning from injury to replace Chris Clark and Rory McArdle.
St Mirren, again without injured midfielder Steven Thomson, also shuffled their pack after the 2-1 loss to Inverness Caledonian Thistle saw them drop out of the top six.
Irishman Carey was preferred to Nigel Hasselbaink, while David van Zanten and David Barron replaced Illias Haddad and former Don Lee Mair.
St Mirren had only won twice on their travels this season and made the worst possible start by going behind after 40 seconds.
Arnason's long throw into the box was flicked on by New Zealand international Fallon to Vernon, who chested the ball down before expertly drilling it into the top corner.
The Dons doubled their advantage after 17 minutes when Fyvie was given too much time and space on the edge of the area to pick out Fallon at the back post, who stooped to head the ball home from only three yards out.
St Mirren pulled a goal back 10 minutes before the break when McLean raced onto a
Thompson header and calmly slotted the ball past Jason Brown for his third goal of the season.
The youngster had a chance to equalise minutes later when he was played in by Paul McGowan, but Jack managed to make a vital block.
The Dons had an appeal for a penalty waved away as the half drew to a close when Vernon fell under pressure from Barron.
The hosts made a positive start to the second half with Vernon heading wide from a Rob Milsom cross before they had a second penalty appeal turned down when Barron challenged Fallon in the area.
The visitors then equalised in spectacular fashion after 52 minutes when Carey unleashed an unstoppable free-kick from 35 yards which crashed into the net off the underside of the crossbar with Brown rooted to the spot.
And the visitors should have taken the lead after 61 minutes when Carey's corner found the unmarked Thompson who could only direct his header wide.
Carey had another chance from a set-piece on the edge of the area after Milsom upended van Zanten, but Brown was equal to the winger's low drive.
At the other end, Vernon was guilty of passing up a golden opportunity when he headed over from a curling Milsom delivery.
Brown produced a magnificent save to deny Thompson as the Buddies ended the game strongly.
But it was Aberdeen who had a goal chalked off in injury time when Samson fumbled the ball into the net from a Fyvie cross.
The midfielder was then shown a red card for dissent following the controversial decision.