Hampshire 177 for 5 (Howell 62*, Smith 3-35) beat Gloucestershire 176 for 9 (Hammond 66, Wheal 4-35) by five wickets
Benny Howell's brutal half-century took down his former Gloucestershire team-mates to keep Hampshire Hawks' Vitality Blast hopes alive.
All-rounder Howell had already taken two wickets as Hampshire fought back to restrict their visitors - who have never won a T20 at Utilita Bowl - to 176.
But he then clubbed four sixes and five fours to equal his T20 best of 62 not out to start a south coast party.
The Hawks' five-wicket win put them four points adrift of the qualification places with three matches to play, while fourth-placed Gloucestershire remain two points behind Essex.
Miles Hammond and Cameron Bancroft saw off a couple of tricky new ball overs before tucking into their work after Gloucestershire had chosen to bat.
Neither flaunted any flair but used timing and a lightning outfield to pick a boundary or two an over - as 49 stress-free runs came in the powerplay.
But where Hammond ticked into gear - albeit surviving a couple of drops - Australia Bancroft came a cropper when Howell chopped one through him to end 92-run stand, Gloucestershire's best opening partnership versus the Hawks.
Hammond went past 350 runs in this year's Blast and a seventh T20 fifty - coming in 36 balls - but the visitors went from looking at setting 200 to an almighty collapse.
All told it saw eight wickets fall in 33 balls, with the vast majority of them caught slogging to fulfil the double-hundred prophecy.
Scotland international Brad Wheal - now the owner of 50 T20 wickets for Hampshire. was the chief destroyer with four wickets. His figures of four for 35 were only ruined by a late six and four from Ben Charlesworth.
Charlesworth was a rare Gloucestershire success in the second half with his 39 off 19 taking them to a par, but under what they had looked set for, 176.
In reply, Ben McDermott started strongly by pumping fellow Aussie down the ground for a maximum, but James Vince strangling a pull shot behind off the last ball of the powerplay stemmed the hosts' momentum.
The following six overs went for 27 runs as Tom Smith led a Boa-like tightening on the Hawks.
Tom Prest reverse swept to point and McDermott and Toby Albert both thumped to long off as Smith struck in his first three overs with analysis of three for 14.
But a switch of ends for his last saw Howell explode with a pair of sixes in a 22-run over to take the equation to 63 off 30 balls, and swung the pendulum.
Howell continued his assault against Marchant de Lange with another two huge hits and was also dropped by wicketkeeper James Bracey - his first Hampshire half-century coming in 22 balls.
Joe Weatherley had been the onlooker for much of the fifty stand and fell when de Lange parted his stumps.
A five-run over from Matt Taylor meant 31 was needed from the last two overs but Howell recharged with James Fuller to make it 14 off the last.
It was taken down to four off the last delivery, which Howell scooped to the boundary to celebrate by ripping off his helmet.
