Formartine came from two goals down to stun Deveronvale with three second half goals in a seven-minute spell to take all three points at Princess Royal Park.
The home side had an early chance after seven minutes when Chris Blackhall held the ball up well and fed Paul Sutherland, but his low cross just evaded Grant Noble in the middle.
In the 37th minute Stuart Anderson fired in a superb delivery from a free kick that was missed by Grant Pennet, came back off the crossbar and was somehow cleared off the line by Lukas Krobot.
Neil Gauld then fired a half chance well wide and Graeme Rodger's effort squeezed past the far post as Formartine pushed for an opener.
It was Vale who went in front on half time when Callum Murray got to the byline and produced a superb cross onto the head of Dane Ballard to score with ease from close range.
Good interplay between Jamie Masson and Scott Barbour saw Rodger poke Scott Barbour's low ball just wide in the 48th minute, then at the other end Noble did brilliantly to set up Sutherland, but he put a weak effort straight at Andy Reid.
Ten minutes after the break Ballard streaked away from the visiting defence and squared an excellent cross for Murray to sweep past Reid from eight yards and put Vale two ahead.
In the 62nd minute Formartine pulled one back, Barbour's corner flicked on by Gauld and headed home by Shane Jamieson.
Two minutes later it was all square when Gauld's cross from the left was superbly hooked into the far corner of the net by Barbour from 12 yards.
Formartine were rampant now and Gauld got in behind again in the 69th minute to lob the ball across for sub Conor Gethins to plant his half volley past Pennet and complete a stunning seven-minute turnaround.
A lucky break of the ball put Gethins through on goal soon after, only for Pennet to save well with his feet.
Gauld missed a glorious chance to put the game beyond the home side when he fired Barbour's cutback wide from only eight yards with 12 minutes left.
Scott Ferries was shown a straight red card for a bad challenge on Zander Jack with nine minutes to go, then with time running out sub Nathan Ross fired a great chance to equalise straight at Reid.