Deane opted to bat first and Rob Woodman and Neil Brand got them away to decent start.
Both were removed by James Hayman who, once again, bowled with real pace and aggression to give Ashcott back on terms.
But then came the telling stand of the game as Australian John Rogers and Somerset's Jack Leach made 73 and 34 respectively as they dominated the Ashcott attack.
Ben Rudge, with four wickets, bowled very well at the death for Ashcott but Deane responded with solid late contributions from Ali Warren and Sam Shaikh, who hit his first ball faced for six.
Deane closed on 161-6 in their 20 overs.
Ashcott openers Steve Tinnion and Gareth Harte racked up 40 runs in just three overs as the Deane’s seam attack struggled to make an impact.
However the introduction of left arm spin from both ends in the form of Brand and Leach put the brakes on the Ashcott charge and from then it was only really Hayman with 27 who kept the Ashcott fire burning as wickets fell at regular intervals and the earlier momentum was never regained.
The last wicket was a run out in the last over as Ashcott needed more than two runs per ball to win and so had to go for broke.
Deane were left 21 run winners, claiming the cup for the first time since 2009.
Rogers was named as Man of the Match and joins Reg Keates of Taunton CC in 2001 and Grant Thompson of Taunton Deane CC in 2009 as overseas players to win the Jack Tucker Memorial Shield.