Ice cool Callum Milne slotted the game-winner five minutes from time as Grange kept their treble dream alive.
The Edinburgh club had to twice come from behind to see off Western Wildcats 3-2.
And the West of Scotland club were seething at a refereeing decision which led to the penalty stroke.
Grange, who have already won the Division One title and the Scottish Cup, were 1-0 and 2-1 down on their home pitch to Western, but will now play
Dundee-based Grove Menzieshill in Sunday’s (4pm) Grand Final.
Milne said: “Somebody had to step-up and take it and it fell to me.”
The 29-year-old added: “It was a relief to see it go in and also to hear the final whistle as Western proved tough to crack.”
Meanwhile, Grove disposed of Bromac Kelburne 5-3, controlling most of the contest at Glasgow’s National Hockey Centre.
Dundee Wanderers now face Uddingston to avoid the drop to Division Two after the Tayside team lost 4-3 after penalties to Watsonians who are now promoted.
A Callum Duke inspired Hillhead sealed their top flight status with a comfortable 5-1 win over Uddingston.
In the women`s play-offs Watsonians were beaten 5-1 in their semi-final against champions Edinburgh University.
The students were two up at the interval through Amy Brodie and Sophie Maunder.
Watsonians pulled one back but further strikes by Brodie, Ellie Halliday and Becky Merchant secured the victory.
Clydesdale Western made the final with a 3-1 win over Grove Menzieshill at Glasgow’s National Hockey Centre.
GHK and Hillhead will play top flight hockey next season with 1-0 and 2-1 victories over Inverleith and Grange respectively.
That leaves the Edinburgh sides to come to Glasgow Green for the Grand Finals with the loser relegated to Division Two.
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