Mark Hardinges steered Gloucestershire to a dramatic two-wicket Pro40 League win off the penultimate ball.
Hampshire posted an imposing 236-4 in a rain-hit match of 35 overs a side but Hamish Marshall (47) and Marcus North (56) kept the Gladiators in the hunt.
Hardinges then crashed two sixes in an unbeaten 27 to clinch victory on the final day of the Cheltenham Festival.
The veteran's efforts sealed the hosts' first win in any competition since a Twenty20 victory at Bristol on 24 June.
Gloucestershire had endured a miserable festival, failing to conjure a win in five matches at the College Ground.
Steve Kirby hinted at a change in fortunes when he bowled John Crawley with his first ball.
But that proved a high point as Michael Lumb (88) put on 116 in 18 overs for the second wicket with Michael Carberry (56), and then added a further 85 in 11 overs with Chris Benham (49).
Marshall accrued 47 in 42 balls and North hit 56 from 52 to lay the foundations for Gloucestershire's first win in four attempts in the 40-over competition.
Pakistani leg-spinner Imran Tahir (3-40) helped reduce Gloucestershire to 189-6 in the 29th over when Hardinges arrived in the middle.
The all-rounder, who has been told he can leave at the end of the season when his contract expires, dug deep and struck the winning boundary off the penultimate ball from Billy Taylor.
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