NCL D2, Hove: Somerset 377-9 (45 overs) beat Sussex 186 (30.2 overs) by 191 runs
Somerset brought a halt to Sussex's celebrations by hitting the highest total ever in the National League.
Captain Mike Burns made 91 and Ian Blackwell smashed 111 from just 56 balls as the Sabres rattled to 377-9.
Hungover from the County Championship celebrations, Sussex were bowled out for 186 in 30.2 overs, suffering a 191-run defeat.
Blackwell chipped in with 3-57 and fellow spinner Keith Dutch took 4-34.
Somerset's total topped the previous record 375-4, hit by Surrey against Yorkshire in 1994 - in a 40-over match.
But Surrey still hold the world record for the highest total in a limited-overs match - 438-5 in a 50-over C&G Trophy match against Glamorgan last year.
It was scant consolation for Somerset, who still finish second-from-bottom in Division Two after a miserable season.
Sussex: R R Montgomerie, M W Goodwin, P A Cottey, T R Ambrose
R S C Martin-Jenkins, M J Prior (Wkt), M H Yardy, C D Hopkinson
M J G Davis (Capt), P M Hutchison, B V Taylor.
Somerset: W J Durston, M J Wood, M Burns (Capt, Wkt), K A Parsons
I D Blackwell, J C Hildreth, K P Dutch, G M Andrew, R L Johnson
S R G Francis, N A M McLean.