Craig McGuffie scored in the last minute of extra time to send Morton through to the Championship play-off final.
McGuffie curled in a superb effort to seal a 3-1 win over Montrose and keep his side's bid to stay in the second tier alive.
Gary Oliver fired Morton ahead, and level at 2-2 on aggregate, before Cameron Salkeld headed them into the lead in the tie.
Russell McLean scored for Montrose before McGuffie's dramatic late heroics.
They will face Airdrieonians, who won an equally thrilling match against Cove Rangers after extra time.
Rangers took the lead on the night and in the tie when Mitchel Megginson sent a glancing header into the top corner in the 15th minute.
But the lead lasted just four minutes before Calum Gallagher got the final touch on a loose ball at the far post to equalise.
A nerve-shredding finale saw Rory McAllister put Rangers ahead before Paul McKay equalised, and Gallagher hit the winner in extra time.
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