Glamorgan have won two of the past four editions of the One-Day Cup, but their defence got off to an inauspicious start in Neath.
They put Hampshire in and watched Gubbins make a career-best List A score in providing the platform for the innings.
He put on 141 with 17-year-old wicketkeeper Ben Mayes, who hit a debut 74, while Felix Organ’s cameo of 32 off 14 balls pushed the total well past 300.
Glamorgan skipper Carlson hit his maiden century with a blistering 135 off 92 balls, which included 10 sixes.
But the next best score was Alex Horton’s 35 and the highest partnership was just 52 as Hampshire kept picking up wickets.
Gloucestershire’s defence of their T20 Blast title may have ended meekly, but their One-Day Cup campaign began well against Derbyshire in Cheltenham.
Price top-scored with 103, while James Bracey (83), Ben Charlesworth (60) and captain Jack Taylor (67) all passed 50 to set up an innings which eventually finished on 341-8.
Derbyshire slipped to 152-4 in the 28th over, before a stand of 76 between captain Brooke Guest, who top-scored with 86, and Amrit Basra (40) revived their hopes.
But both fell to Zaman Akhter as he took four wickets in three overs to effectively seal the win. He ended with 4-47 as Derbyshire were bowled out for 282.
Nottinghamshire were in trouble as Essex’s Jamie Porter reduced them to 41-4 in the match at Nettleworth in a 10-over spell of 4-29.
But Moores and Australia all-rounder Daniel Sams (45) put on 137 for the sixth wicket, with Moores smashing his previous highest score of 76 by almost double.
Rain reduced Notts’ innings to 46 overs, with Essex handed a DLS target of 286 off the same allocation.
Robin Das and Simon Fernandes each hit 46, but wickets fell at regular intervals with the visitors bowled out for 234 with 4.5 overs remaining.
