Delray Rawlins hit a superb unbeaten 35 as Sussex Sharks secured a three wicket victory over Gloucestershire at the Bristol County Ground with two balls remaining.
Gloucestershire players protested in vain when they incurred a six-run penalty for a slow over-rate, leaving the visitors to score seven off the final over.
Rawlins then kept his cool to knock off the winning runs, finishing with five fours and a six from a 17-ball innings which ultimately proved decisive.
Ian Cockbain had earlier scored 61 not out, sharing in stands of 67 and 38 with James Bracey and Benny Howell for the third and sixth wickets respectively as the hosts raised 159-6 after being put in.
Having successfully chased to beat South Group leaders Kent by nine wickets in their previous outing, Sussex again elected to field first. That looked a good decision once new-ball bowlers Ollie Robinson and Reece Topley accounted for openers Miles Hammond and Michael Klinger in quick time as Gloucestershire's top-order again fell short of expectations.
Gloucestershire enjoyed a much-needed stroke of luck when James Bracey was dropped at cover point on one by Rashid Khan off the bowling of Chris Jordan. He certainly made good his escape, posting 30 from 26 balls and staging a restorative stand of 67 in 9.1 overs with Cockbain for the third wicket.
Sussex deployed spinners Khan and Danny Briggs in tandem in an attempt to stem the flow of runs, a ploy which accounted for Bracey and the dangerous Ryan Higgins and caused Gloucestershire to lose crucial momentum during the middle overs. Briggs' dismissal of Bracey saw him become the leading wicket taker in the history of English domestic T20 cricket.
Heavily dependent upon Cockbain, Gloucestershire were indebted to the Liverpudlian, who punished anything short of a length in raising 50 from 41 balls to keep his side in the game.
When big-hitting Jack Taylor missed a straight delivery and was pinned lbw by Jordan in the 16th over, it was left to Benny Howell to provide late acceleration, the veteran all-rounder scoring at two runs a ball in a valuable sixth wicket stand of 37 before holing out to long-on off Robinson in the final over.
Cockbain finished unbeaten on 61 from 49 balls, with 5 fours and a six, but not even his innings could dispel the feeling that Gloucestershire had fallen short of requirements.
But Sussex found the going equally difficult on a two-paced pitch, Philip Salt and Laurie Evans succumbing to David Payne and Tye respectively as Gloucestershire made good use of the new ball.