Ian Cockbain smashed 84 off 51 balls and Graeme McCarter finished with five wickets as Gloucestershire edged Sussex Sharks by four runs, the hosts falling just short of their victory target in a thrilling finale at the BrightonandHovejobs.com County Ground.
Having found themselves 111 for six in the 13th over in pursuit of 190, Sussex - largely thanks to Will Beer's 17-ball 37 and Steffan Piolet's 25 from 20 - launched a spirited fightback in this NatWest T20 Blast South Group clash.
But it all unravelled in the final over as, needing 10 to win and with three wickets in hand, McCarter claimed three wickets to end the match with a limited-overs-best 5-35 and crush the home team's hopes of an unlikely triumph.
Cockbain's superb knock earlier included eight fours and three sixes, and helped the visitors post 189 for six.
Yasir Arafat was the pick of the Sussex bowlers with 3-38, while Piolet finished with 2-39 - seeing off opener Michael Klinger for 28 and then stopping Cockbain's rampage.
Alex Gidman was the first to fall, bowled by Arafat for 11, setting the platform for captain Klinger and Cockbain to share a 102-run stand which provided more than half of Gloucestershire's total.
Their partnership came to an end when Klinger lofted Piolet to long-off, where Beer pulled off a fine catch to leave the visitors 115 for two.
— Clare Connor (@ConnorCricket) June 6, 2014
Benny Howell contributed two runs before belting a full-toss back at bowler Chris Nash, who held on at the second attempt.
Cockbain's fine innings ended in the next over when he holed out to Ed Joyce off Piolet.
Arafat bowled Geraint Jones for 13 and Hamish Marshall for 24 in the closing overs, but Dan Housego and Jack Taylor - the latter clubbing a six despite facing just two balls - the not-out batsmen at the end.
Rory Hamilton-Brown hit 49 from 32 balls in response, letting loose with five fours and three sixes.
His dismissal from the final delivery of the 12th over with the score on 106 looked to have signalled the beginning of the end for the home team, before their late rally.
McCarter gave Sussex their breakthrough with two wickets in two balls at the start of the fourth over, first bowling Luke Wright and then having Joyce chip to Howell at mid-on.
Opener Matt Machan shared a 51-run third-wicket stand with Hamilton-Brown but, having registered 34 from 24 balls, sliced to Tom Smith at short third man off Taylor.
Hamilton-Brown fell when he top-edged to McCarter at third man off Howell.
Ben Brown then reverse-paddled to McCarter at third man to fall and Arafat was caught and bowled - also for nought - as Taylor claimed two wickets in three balls in the 13th over to seemingly put Sussex on the ropes.
However, the home tail wagged. Nash was run out by Howell for 20, but Piolet and Beer continued to make hay until the final over, when the pair - and number 10 Chris Liddle - were all caught in the deep by Housego off McCarter.