Tony Wallace converted an 88th-minute penalty as Annan set up a Scottish League One play-off final clash with Edinburgh following a 2-1 aggregate win over Forfar.
Wallace pounced after Ross Meechan was penalised for a foul, cancelling out Stefan McCluskey’s first-half opener for Forfar just as the tie appeared to be heading for extra time.
Forfar, trailing 1-0 from the first leg, came agonisingly close to taking the lead in the 13th minute when Craig Slater’s free-kick hit the underside of the bar.
But McCluskey opened the scoring in the 32nd minute, tapping home after Tomas Brindley squared the ball into his path.
Forfar keeper Marc McCallum produced a stunning double save to deny Dominic Docherty and Wallace, while Annan’s Greg Fleming tipped Callum Moore’s effort onto the bar and pulled off an incredible stop to keep out a Gary Harkins header before Wallace struck the decisive blow.