Holders Gloucestershire set off on another cup run, helped by a career-best effort from Matt Windows.
The opener had never hit a half-century in this competition but he cracked 82 to soothe his side's nerves against the Sussex Cricket Board at Horsham.
Windows' gritty 123-ball innings provided the backbone of Gloucestershire's total of 238-9 and earned him the gold award as the visitors won by 95-runs.
Initially Gloucestershire didn't have things all their own way after being put in by home skipper Richard Halsall on a slow track.
Kim Barnett was bowled for eight by John Morgan, whose pace and accuracy were rewarded with figures of 2-30 in his 10-overs.
Ian Harvey blasted 23 off his first 12-balls before seeing his top-edged sweep superbly held by Paul Stevens, one of three catches for the Sussex CB fielder who normally keeps wicket.
Chris Taylor (25) and Mark Alleyne (22) also chipped in, while spinner David Hussey took 3-28 and seamer Danny Alderman sent down 10 tight overs for just 23.
James Averis ripped the heart out of the Sussex CB's reply by bowling George Campbell and Hussey for ducks in the first over.
Mike Cawdron followed suit with two wickets in his first over as the Board were reduced to 37-5.
Carl Hopkinson (45), on his home ground and Chris Mole (41) raised home hopes by pulling and driving their way to an attractive partnership of 64, the biggest of the match, before the Board were finally bowled out for 193.
Averis, Cawdron, Harvey, Alleyne and Ball shared the bowling honours with two wickets apiece as the one-day kings enjoyed an ultimately comfortable day in the West Sussex sunshine.
Hopkinson and Mole's resistance too late to deprive Gloucestershire
Gloucs vs Sussex CB
England League Cricket
England Domestic Season
Horsham Cricket and Sports Club