In a thrilling match, Glamorgan scored 247 for 9 with standout performances from Douthwaite (55), Ingram (47), and Root (46), while Barnard was the pick of the bowlers for Warwickshire with figures of 4-34. Warwickshire put up a strong fight but were ultimately bowled out for 208, with Burgess top-scoring with 85. McIlroy was the most successful bowler for Glamorgan, taking 3-42. In the end, Glamorgan emerged victorious, winning by a margin of 39 runs.
Dan Douthwaite turned into a matchwinner with both bat and ball as he guided Glamorgan into the Metro Bank One-Day Cup final at Trent Bridge next month with a 39-run victory over Warwickshire at Sophia Gardens.
It was his lusty batting that first caught the eye as he hauled the home side through to a 50-over total of 247 for 9 after they had earlier been floundering at 44 for 4 in the 15th over. He hit four sixes - one out of the ground and into the River Taff - in his sparkling 55, hitting 16 off the final over from Oliver Hannon-Dalby.
Prior to that Colin Ingram (47) and Billy Root (46) had steadied the innings. Then Douthwaite got into his bowling rhythm and removed Chris Benjamin and Kai Smith to catches at the wicket by Will Samile as he reduced the visitors to 62 for 6 in reply in the 21st over. They were eventually all out for 208.
Timm van der Gugten, who had earlier scored 26 with the bat, picked up the wickets of Rob Yates (4) and Will Rhodes (4), while fellow paceman Jamie McIlroy got rid of the dangerous Ed Barnard (14) and Hamza Shaikh (8).
Tight bowling and energetic fielding by the home side turned the screw on Warwickshire as the run-rate climbed to more than seven per over in the 26th over. The 100 came up in the 32nd over as the rate rose to more than eight per over.
Michael Burgess was the only batter to provide some solid resistance in the middle order and he reached his half-century with a six off the spin of Ingram. He obviously enjoyed the experience as he hit the next two over the boundary for maximums.
His seventh wicket stand with Jake Lintott reaped 87 runs and his 85 contained four sixes and six fours. His departure, caught at mid off by Douthwaite off the bowling of the returning McIlroy, left Warwickshire at 149 for 7 - still 99 short of their target with 11 overs to go.
When Lintott was caught off a reverse sweep of the bowling of Ben Kellaway for 26 the game was up. There were a few big hits in defiance at the death - Michael Booth hit three sixes - but Warwickshire ended 40 runs short of the victory target.
Warwickshire captain Barnard had no hesitation in asking Glamorgan to bat when he won the toss. Playing on the same Sophia Gardens wicket as used for the home side's win last week over Yorkshire that earned them a straight semi-final tie, Barnard had obviously taken note of the help the pitch had given the seam bowlers in that match.
It proved to be a good choice for the seam attack that he led. Opening the bowling and running straight through his allotted 10 overs, the visiting skipper ripped through Glamorgan's top order and ended with 4 for 34 in his top-class spell.
Three of his victims were caught in the slips by Rob Yates - Asa Tribe (13), Kiran Carlson (2) and Will Smale (13) - and he trapped Sam Northeast (8) lbw. That reduced the home side to 4 for 44 in the 15th over and he could have had a fifth wicket had Yates not put down an easy chance Colin Ingram in the 17th over.
At that stage the Ingram had only scored 18 and he went on to notch 47 before he was fifth out, trapped lbw by Michael Rae. Ingram steadied what looked like being a sinking ship in tandem with Billy Root as they put on 46 for the fifth wicket.
Building on his midweek half-century in the win over Yorkshire Vikings, Root five fours in his 46, sharing in invaluable stands of 55 with Ben Kellaway and then 22 with Douthwaite before his departure in the 40th over made it 167 for 7.
At that stage Warwickshire must have been hoping to mop up the tail quite quickly, but Douthwaite, van der Gugten and Andy Gorvin had other ideas. Between them they conjured up 92 runs as they plundered 79 off the last 10 overs to set the visitors a target of 248.
Douthwaite ended on 55 and thumped four enormous sixes and four fours as he took 15 and then 17 off the final two overs. That meant the Welsh side at least had some sort of total to defend - which they managed to do with a few overs to spare.