Dolphins dominated from the outset and hit the woodwork no fewer than three times before Dan Cann netted the opener late in the first half.
Plucky Hammers did all they could to force a leveller in the second half but rarely got in behind their resolute opponents, who made sure of the silverware through Carl Preston’s breakaway goal with two minutes to play.
There was still time for Dominic Allen to see a penalty saved by Poole keeper Nick Hutchings to compound the Wessex League club’s misery.
Following a lively start, Cann showed good strength to lay off for onrushing midfielder Carl Pettefer who blasted high and wide when well placed.
Dolphins struck the frame of the goal for first time when Marvin Brooks outmuscled his marker at the far post to reach Preston’s centre as the Southern League outfit continued to make most of the running.
Charlie Davis’s marauding run ended with a deflected effort brushing the crossbar midway through the half before the lively Preston sent in a fizzing low centre which just evaded Ekow Elliott as Poole bossed the first-half exchanges
Tom Killick’s men were left cursing their luck once more as Preston’s delicious free kick pelted the base of the post after half an hour.
But the opener was never likely to be far away and after another driving dash down the right, Davis teed up Cann to swivel and find the bottom corner with a crisp low shot on 34 minutes.
For all their hard work, United struggled to fashion opportunities but almost levelled on the stroke of half-time when Russell Cook hit a sweet half-volley from the edge of the area which Hutchings did well to hold.
The second half was tame by comparison but Poole eventually kicked into gear again and had two presentable opportunities to double their advantage just after the hour.
Tenacious youngster Billy Lowes drove through midfield and played a smart one-two with Elliott but his soft shot was smothered by Nick Thomas.
Seconds later, Preston centred for Brooks but the midfielder somehow made a meal of hid far-post finish, while substitute Jon Davies fired wide on the half-volley following good work from Cann and Brooks.
Hamworthy prospect Alex Martin bamboozled two defenders with a mesmeric run but could not provide a finish when his under-pressure team-mates needed it most.
But United’s golden opportunity was still to come. With five minutes to play, Hutchings could only punch a deep free kick as far as substitute Lee Diaper but the winger skewed horribly wide of the unguarded net from 20-plus yards.
Graham Kemp’s men were made to pay for that profligacy with two minutes to play as a simple ball down the left channel saw Preston get the better of Billy Walker before his bobbling low shot nestled inside Thomas's far post.
United knew it was not to be their night when moments later, Lamin Dibba tangled with former Dolphins frontman Cook in the box, but after a long delay Allen’s spot kick was comfortably smothered by Hutchings, a moment which summed up Hammers' fortunes on the night.
Dolphins: Hutchings, Davis, Swindlehurst, Dibba, Whisken, Pettefer (Parrett, 90), Elliott (Davies, 65), Lowes, Brooks (Turner, 73), Preston, Cann. Unused subs: Devlin, D Thomas (g/k).
Hammers: N Thomas, Penny, Legg (Diaper, 69), Walker, Haysom (Miles, 79), Corby, Allen, Hester, Osborne (Yelland, 56), Cook, Martin. Unused subs: Sturgess, Horlock.