Somerset 131 for 2 (Myburgh 75*, Hildreth 35*) beat Surrey 129 (S Curran 30, C Overton 4-27) by eight wickets
Five thousand South London schoolchildren, boosting the Kia Oval crowd as part of Surrey's annual Schools' Day, saw Somerset trounce their local heroes by eight wickets after skittling Rory Burns's team for just 129 in 35.2 overs.
Craig Overton took 4 for 27 in two spells, including a new ball burst of 3 for 16 in six overs, and Peter Trego picked up 2 for 23 in ten skilful and controlled overs from the Vauxhall End.
It then took Somerset just 21.3 overs to knock off the runs, with Johann Myburgh finishing on a punishing 75 not out from 65 balls, with 13 fours, as they got their Royal London One-Day Cup South Group campaign off to the perfect start.
Sam Curran did sent back both Steven Davies, caught off a leading edge for 12, and Trego, leg-before second ball for a duck, in his third over, but Myburgh and James Hildreth then added an unbroken stand of 96 in just 16 overs with Hildreth also playing some attractive shots in his unbeaten 35.
It was Somerset's fourth successive Royal London Cup victory against Surrey but from the home side, beaten Lord's cup finalists in each of the last three years and one of the fancied teams in the competition again this season, it was an abject performance.
Put in on a two-paced pitch, they were 12 for 3 before the end of the fourth over and never came to turns with the discipline needed batting first on such a surface. Poor or over-ambitious strokes were compounded by the unnecessary run out for 0 of Scott Borthwick, who came in at No 7 rather than in the top order as he does in championship cricket.
Will Jacks, a 19-year-old graduate of Surrey's prolific Academy, was sent in to open with Dean Elgar and made just 3 before, in the second over, he lifted a drive at Overton to extra cover.
South Africa Test opener Elgar was next to go, in the third over, steering Lewis Gregory to backward point on 1, and Ollie Pope, in at No 4, got a leading edge as he tried to drive Overton towards mid on and was athletically caught for 0 by Max Waller, sprinting in five yards and also diving forward from a deepish mid off.
Ben Foakes quickly reached 21, with some pedigree strokes, before he was unfortunate to edge a legside ball from Overton to keeper Davies.
That was 41 for 4 and it got even worse for Surrey when, on 50 and 58 respectively, skipper Burns chipped Trego to mid on to go for 17 before Borthwick, playing Trego to mid on, called for a sharp single but saw his partner Curran fail to respond. He was left stranded at the bowlers' end.
Curran played some nice shots in his 30, the top score of the innings, but saw Rikki Clarke hit a short ball from Trego high to deep mid wicket on 9 before he himself was caught behind in the next over, the 27th, as he drove at Gregory to leave Surrey 84 for 8.
The tail at least took Surrey into three figures, with Gareth Batty (14) leg-before to Tim Groenewald aiming an ugly smear and Jade Dernbach swinging the same bowler for a mighty six over long on before skying Overton to cover on 12.
Stuart Meaker remained 18 not out but Surrey's final total was never going to be enough and the match was over by 3.45pm - the finish delayed by a scheduled 45-minute interval, taken when Somerset were 81 for 2 from 14 overs.