Tommy Craig's side looked set for a seventh defeat in eight top-flight games after goals from Mark Reynolds and Peter Pawlett put the hosts in the driving seat.
But St Mirren showed remarkable resolve to battle back, as Callum Ball's strike and a late Kenny McLean penalty ensured the spoils were shared.
Aberdeen - who would have gone above champions Celtic and into fourth with a win - controlled the first half but had to wait until the 45th minute for Reynolds to fire them ahead from 12 yards after a scramble in the box.
Jonny Hayes then laid on a superb cross for Pawlett to grab his fourth of the season in all competitions in the 56th minute.
That two-goal cushion lasted just a minute, however, as Ball turned in Gregg Wylde's delivery from a tight angle.
And the comeback was complete four minutes from time, McLean keeping his cool to convert from the spot after Reynolds was adjudged to have handled John McGinn's cross.
St Mirren remain second bottom and Aberdeen stay sixth.
