A 4-1 victory for the 29-year-old from Banbury prevented Fisher, the world No 1 and world champion, from winning her fourth tournament in a row.
"I am just pleased to play well with a trophy on the line because I haven't been doing myself justice in finals," said Davidson, who is now sure to improve on her current position of No 12 in the world rankings.
Davidson, who runs a mobile fish and chip shop with her husband, retired from the game for a time but since her return she has been runner-up in both the Regal Welsh Open and Regal Women's Masters.
After losing the opening frame to Fisher, Davidson, assisted by a 54 break - the highest of the match - moved into a 2-1 lead. Davidson crucially snatched the fourth frame with a green-to-black clearance before completing her surprise victory by edging a tense 35-minute fifth frame on the blue.
In the semi-finals, Davidson had squeezed through 4-3 after the world No 2, Karen Corr, went in off the black in the deciding frame.
The world No 3, Lisa Quick, from Weston-super-Mare, built the highest break of the championship, 98, in the last 16.Reuse content