A first-wicket stand of 144 between Luke Wright (77) and Phil Salt (63) helped Sussex beat Glamorgan by 33 runs in the Vitality Blast.
The two openers guided their side to an imposing total of 201 for eight which was always going to be difficult to chase.
And so it proved as Glamorgan were all out for 168 with David Lloyd making 51. Sussex’s 16-year-old leg spinner and man of the match Archie Lenham continued his fine Blast form with four for 26.
A second defeat in as many days leaves Glamorgan needing a miracle to make the quarter-finals while Sussex remain in the qualification mix.
Sussex won the toss, chose to bat, and made a rollicking start.
Wright smashed a straight six over long on but his opening partner Salt was just as aggressive as Glamorgan’s bowlers were put to the sword.
Sussex reached 77 without loss after just six overs as both batsmen peppered the boundary.
Wright went to 50 from just 24 balls and the 100 came up in only the ninth over. Salt’s half century came from 28 balls with eight fours, but he was finally cleaned up by Dan Douthwaite.
Wright immediately followed him back to the pavilion in the same over when he was caught behind by Chris Cooke for 77 from 41 balls.
Sussex were still primed for a huge score at 154 for one with seven overs to go, but Ravi Bopara made just 12 and their middle order struggled to replicate their opening pair’s heroics.
David Wiese failed and Harrison Ward went first ball, but consecutive sixes from Australian Travis Head (26) helped Sussex past 200.
Douthwaite finished with impressive figures of three for 28.
Glamorgan took 16 and 12 from Mitchell Claydon’s and Tymal Mills’ first overs in response as Lloyd started with a bang. It helped Glamorgan to 61 without loss from the first six overs.
Lloyd was more aggressive than partner Kiran Carlson who was the first to go, caught at long on by Head in Bopara’s first over.
Sussex waited until the eighth over to introduce Lenham, but his first six balls went for just four runs. Glamorgan then needlessly lost Colin Ingram, run out for three.
Lloyd went to 50 from just 27 balls but when he was superbly caught on the square-leg boundary by Will Beer off Lenham, Glamorgan were 82 for three at the halfway stage.
Douthwaite (35) did hit Bopara into the River Taff and the Sophia Gardens changing rooms for back-to-back sixes, but Lenham got him and James Weighell too as Sussex were comfortable winners.
After the game, Sussex leg spinner Archie Lenham, who was man of the match and took four for 26, said: “I just try to bowl my way and pick up a few wickets for the side.
“I just wanted not to go for a boundary, to keep the run rate down, and hopefully Dan Douthwaite might hit the ball up in the air and get caught. I thought it was going for six at first but David Wiese is a tall guy and it was a great catch in the end.
“It’s pretty amazing. At the start of the season I never thought this would be happening. I was so in the moment when I was bowling at Douthwaite. It’s an amazing experience for me to play in this side and the other players are great to play with.”
Glamorgan batsman David Lloyd, who top scored with 51, added: “It was always going to be a tricky chase after their first innings.
"We got a really good start but lost wickets at key times. Wright and Salt are two very, very good players who can do that to an opposition, but I think we showed character to claw it back and keep them to 200 because they could have got a lot more.
"The luck has gone against us in the last couple of days. I feel good and it’s nice to contribute, but today needed me to get a big score. It’s been very disappointing for us. We have shown glimpses of what we can do, but going forward we need to contribute as a team not as individuals. Things just haven’t clicked.
"Archie Lenham looks very young, doesn’t he? But fair play to him, he shows a lot of character and today he bowled really well even though leg spin is a tricky trade. He looks very comfortable."
More reaction from Luke Wright, who spoke to BBC Sussex Sport's Adrian Harms, can be heard below:
Sussex Cricket are delighted to announce the appointment of former players, Chris Adams and Tony Cottey, to the club’s cricket committee.
Sussex Cricket is thrilled to announce the appointment of Grant Flower as the club’s batting coach.
Grant arrives at The 1st Central County Ground with over a decade of coaching experience at international level.
Sussex’s George Garton and Tymal Mills have been called-up to a 16-player squad for the England men’s International Twenty20 matches against West Indies next month.