Somerset, who have won two of the past three T20 titles, looked down and out when they needed 80 runs from 27 balls to beat Yorkshire.
The target of 162 set by the Tykes was the lowest in T20 matches at Headingley this season by 31 runs.
Only Adam Lyth (64), with a third half-century of the campaign, had troubled the scorers for Yorkshire as Somerset’s bowlers shared the load – Jake Ball taking 3-30 and two wickets apiece for Riley Meredith (2-27), Daniel Sams (2-29) and Craig Overton (2-36).
The hosts then tore into Somerset in their first meeting in this format, quickly reducing the holders to 28-4 in their sixth over.
Tom Banton, released by England to play the game, fell for just one, as did brothers Thomas and James Rew.
Will Smeed (21), Tom Kohler-Cadmore (2), skipper Lewis Gregory (19) and Daniel Sams (0) soon followed to leave Somerset 59-7 and requiring 103 to win from eight overs.
Overton then staged an almost unthinkable recovery, hitting eight fours and five sixes on the way to his first T20 Blast half-century, to inflict a painful defeat on Yorkshire, whose wait for a first title goes on.