|Glamorgan 159-8 (20 overs): Lloyd 81; Kulasekara 4-28|
|Sussex 113 (18.3 overs): van der Gugten 4-17|
Opening bat David Lloyd and paceman Timm van der Gugten played star roles as Glamorgan beat Sussex by 46 runs.
Lloyd led the Glamorgan charge as he blasted 81 off 55 balls, but found little support as Sri Lankan seamer Nuwan Kulasekara claimed 4 for 28.
Sussex lost regular wickets and never threatened to reach their target of 160, as van der Gugten took 4 for 17.
Glamorgan have six wins from seven completed matches.
The second biggest home contribution came from captain Jacques Rudolph with 24 off 12 balls, before the closing seven overs yielded just 36 runs.
Glamorgan fell away badly against a powerful Sussex attack including England pair Chris Jordan and Tymal Mills.
But the home seamers started equally impressively with just one boundary in the opening six power-play overs.
Van der Gugten was backed up by Michael Hogan, Graham Wagg and Craig Meschede with two wickets apiece.
Glamorgan, who face fourth-placed Middlesex on Friday, 8 July at Richmond, move to within two points of south group leaders Gloucestershire with two games in hand.
Glamorgan opener David Lloyd told BBC Wales Sport:
"It's a funny old game, you can go from 97 to nought and now 81, but hopefully I can keep this run going for a bit longer - it was one of those wickets where you had to get yourself in and then take advantage of the bad ball.
"We thought we were about thirty under par, so to bowl them out as convincingly as we did, we're very pleased and hopefully we can take that into the Middlesex game.
"Sussex are probably one of the strongest teams in the league, so to beat them is a real bonus for us.
"We play (leaders) Gloucestershire at home on Sunday, so if we do get a positive result (against Middlesex) and again on Sunday, we should be more or less qualified hopefully."