Glamorgan 225 for 8 (Carlson 60, Root 50, Bethell 4-39) beat Warwickshire 221 (Burgess 73, Benjamin 50) by two wickets
Lukas Carey was the hero at Sophia Gardens for the second time in three days as he once again hit the winning runs to snatch victory for his side.
On Tuesday it was his 29 not out that steered the Wales Minor Counties team to victory over Glamorgan in a friendly and two days later he hit successive boundaries to secure a two wicket win for the Welsh county over Warwickshire in the first round of the Royal London Cup with two balls to spare.
The visitors were defending a total of 26 runs in the final five overs and some brilliant death bowling by Ryan Sidebottom and Ethan Brookes looked as though it might pull off an unlikely win as they conjured up 11 dot balls in that vital period.
A lusty six hit by Roman Walker off Brookes in the penultimate over eased the pressure on the home side, but the game was still in the balance as Sidebottom roared in against Carey with five runs still needed from the last over.
Sidebottom had only conceded a single bye in his previous over against the 24-year-old Carey and started with two dot balls to heighten the tension. Then Carey just reached the mid off boundary with a far from convincing drive and then walloped the next ball past the bowler to complete a two wicket triumph to give Glamorgan the perfect start to their Group B campaign.
Jacob Bethel's white ball debut for Warwickshire saw him capture four wickets to keep his side in the hunt. The Barbados-born former Rugby School pupil was caught at the wicket for a mere two runs in Warwickshire's total of 221, but hit back after coming on as first change to capture 4 for 39 off a terrific spell of 10 overs.
Having dismissed opener Nick Selman he then removed home danger man Kiran Carlson for 60 before setting up a hat-trick attempt after removing Callum Taylor and Tom Cullen in successive. He ended with 4 for 36 from his full 10 overs..
Warwickshire won the toss and opted to go in first on the same wicket on which Glamorgan had been beaten in a one-day warm-up game against the Wales team earlier in the week.
Michael Hogan opened with a maiden, but saw Billy Root drop the dangerous Ed Pollock at first slip in his second over. Pollock reacted positively to his second chance and hammered Carey for a six and two fours in the next over before being caught at point by Joe Cooke for 15.
That made it 21 for 1 and by the end of the 10-over Powerplay the visitors had reached a modest 47 runs and had also lost Matt Lamb. South African youngster Chris Benjamin then took up the cudgel and reached his half-century off 55 balls.
Two balls later he was on his way to the pavilion have gifted a catch to Nick Sleman a catch at deep mid on off Taylor. The 100 came up with a wide off Carey in the 21st over, but with the very next ball he dismissed Bethell with an equally wide delivery that the left hander tickled into the gloves of the diving Tom Cullen.
When Cooke clean bowled Ethan Brookes for two to make it 109 for 5, Glamorgan's stand-in skipper Kiran Carson must have been licking his lips. But opposing captain Mike Burgess dug in and found a useful ally in the 17-year-old debutant Ashish Chakrapani.
Burgess reached his half-century in 73 balls with successive fours off Hogan and by the time Chakrapnai holed out at deep mid wicket for 18 he had helped put on 60 runs. Burgess then went for a career-best 73 in white ball cricket as his side reached 221 before they were bowled out.
Glamorgan's new Kiwi international signing, Hamish Rutherford, lasted only eight balls on his debut and the home side lost two more of their top order batsmen with the score on 41 to tumble to 41 for 3.
That brought Billy Root to the crease to partner Carlson and between them they got to grips with the Warwickshire attack. Carlson's 50 came up in the 31st over off 60 balls, and included five boundaries, and the century partnership arrived after the pair had been together for 21 overs in the 33rd.
Offspinner Bethell was then switched to the River Taff end and on his return to the attack he captured the wicket of Carlson for 60 to open the game back up. Glamorgan still needed 80 runs to win in 16 overs, but their talisman had gone.
Bethell took two more wickets, Root reached his 50, but was then got caught and Joe Cooke made an important 22. That left Roman Walker and Carey to reach the finish line with a stand of 27.