Match scores (Taunton)
Hampshire beat Somerset by four wickets
Somerset inns: 249 (44.2/50 overs. Elgar 78, Trego 55, Hose 50; Berg 3-44, Edwards 2-57, Crane 2-66)
Hampshire inns: 250-6 (37.2/50 overs. Rossouw 156; Overton 4-64)
Match report
Rilee Rossouw blitzed his way to a career-best 156 as Hampshire beat Somerset by four wickets in the Royal London One-Day Cup.
The South African opener stayed at the crease almost to the end as his side became the first team to beat Somerset in this season's competition.
Replying to Somerset's 249, which included half centuries from Dean Elgar, Pete Trego and Adam Hose, Rossouw led Hampshire to the brink of victory, which Lewis McManus then secured with more than 12 overs to spare at Taunton.
After fellow opener Tom Alsop departed without scoring in the fifth over, Rossouw shared a second-wicket stand of 114 with James Vince, who made 35 before falling to Tim Groenewald.
Rossouw was scoring quickly and the 27-year-old reached a 73-ball century with a boundary to square cover off Roelof van der Merwe.
Hampshire were within touching distance of their target when Jamie Overton, who had suffered in his earlier overs, returned and picked up four quick wickets, including that of Rossouw, but only after he had passed 150 and made the outcome a formality.
And McManus smashed successive sixes from the next over to confirm victory.
Earlier, Somerset were rescued from one for two to 86 for two by Elgar and Trego, who was put down in the slips on one.
Trego reached his 50 with a square drive off Berg, but five runs later he was out when the same bowler got his revenge.
Elgar continued, reaching his fifth half-century in as many innings when he took a single off Mason Crane.
Hose played the shot of the day when he drove Edwards to mid-wicket as he reached his second 50 of the competition this season, but he did not add another run before holing out to long off.
Van der Merwe hit two big sixes before he was run out for 19 after a mix up with Elgar.
Craig Overton and Josh Davey went cheaply and when Elgar was out for 78 trying to run Crane down the third man Somerset found themselves 224 for nine.
Jamie Overton played some lusty blows before being bowled by Edwards and Somerset were all out for 249 off 44.2 overs.