Michael Carberry struck an unbeaten century as Hampshire inflicted a third straight Clydesdale Bank 40 defeat on Somerset.
Somerset, runners up in this competition in each of the last two years, posted a total of 212-9 after being asked to bat first at Taunton.
In-form Nick Compton top scored with 81 and shared a fourth-wicket stand of 121 with Jos Buttler (71) to lead the home side out of early trouble at 25-3.
But openers Carberry and Jimmy Adams hammered 103 in 14.1 overs at the start of Hampshire's reply to turn the run chase into a formality.
Craig Overton did manage to dismiss Adams for 56 but Carberry, who hit 14 fours and a six in his 103 not out, polished off Hampshire's nine-wicket success alongside James Vince (44no).
Hampshire sit top of Group B with three wins out of three, while the opposite is true of Somerset.