Surrey 269 for 5 (Jacks 80, Burns 68) beat Glamorgan 266 for 8 (Brown 98, Clarke 3-49) by five wickets
A crowd of almost 5,000 at the Kia Oval were given another glimpse of Will Jacks' immense potential as the 19-year-old struck a brilliant 80 from 57 balls as Surrey eased to a five-wicket Royal London One-Day cup victory against the South Group's bottom side Glamorgan.
Sadly for Surrey, however, their fourth win of the competition did not earn them a quarter-final berth because Essex Eagles beat Kent Spitfires at Chelmsford to go through to the knockout stage alongside Kent and top-of-the-group Hampshire.
Like Jacks, it was also a bittersweet day for another youngster, 21-year-old Glamorgan batsman Connor Brown, who earlier hit a six and nine fours to reach 98 from 136 balls in just his third List A appearance before being caught in the last over.
But Glamorgan's 50-over total of 266 for 8 was never going to be enough after Jacks and Jason Roy plundered 77 in only 8.3 overs for the second wicket to take full advantage of the initial ten-over Powerplay following the early dismissal of an out-of-form Mark Stoneman.
Jacks, who also scored 121 against Gloucestershire earlier in the competition, reached his fifty from a mere 30 balls and pulled Timm van der Gugten powerfully for successive sixes in the eighth over of Surrey's reply. With Roy also swinging Carey over deep square leg for six, it was only when off spinner Andrew Salter was introduced that Surrey's cavalier progress was slowed.
Salter bowled Roy for 23 with his second ball, when brought on for the tenth over, to leave Surrey 84 for 2, and then he also ended Jacks' sparkling knock when the tall opener yorked himself as he advanced to drive. Jacks had hit 12 fours, besides those two huge sixes of Van der Gugten.
From 125 for 3, it was left to Surrey captain Rory Burns and the classy Ben Foakes to steady Surrey with a fourth wicket stand of 79 in 14 overs.
Both got out when victory was all but assured, Burns for a 69-ball 68, caught at long on off David Lloyd's off breaks, and Foakes held at mid wicket off Carey for 30.
Ollie Pope and Sam Curran, in an unbroken sixth wicket stand of 51, completed the win with 9.2 overs to spare.
Rikki Clarke, with a deserved 3 for 49, was the most successful bowler in a disciplined Surrey attack in which Morne Morkel looked a class apart while taking 2 for 39 from his ten overs. Tom Curran had a rare off day as he was taken for 80 from his ten-over allocation.
Glamorgan lost their first two wickets without a run on the board, as openers Nick Selman and Aneurin Donald fell to Morkel and Sam Curran respectively to the third and tenth balls of the match.
Glamorgan's recovery was launched by Brown and Colin Ingram, the captain, who put on 85 in 18 overs for the third wicket but Ingram then aimed a reverse sweep at off spinner Batty - perhaps an error of judgement on the left-hander's part at that stage of the innings - and was lbw for 44.
Ingram had faced 59 balls, hitting sixes off both Batty and Tom Curran, but his dismissal was quickly followed by that of Lloyd, who was caught at long leg in the 25th over when Morkel returned for a quick second burst.
Brown was fortunate to squeeze a searing Sam Curran yorker off the toe of his bat just past Foakes for four to go to his half-century but he and his fellow youngster, the 20-year-old Kiran Carlson, added 65 to give Glamorgan the chance to post some sort of defendable total.
Carlson was leg-before to the accurate Clarke for 33 but Brown, accelerating, pulled Sam Curran for six and then swatted Morkel over mid off for four to go into the 80s.
Graham Wagg proved to be just the man Glamorgan needed to join Brown, swinging three legside sixes in a violent 18-ball 35 before he skied Clarke to extra cover.
Brown, needing just two for his first List A hundred, selflessly swung the second ball of the final over, bowled by Clarke, to deep midwicket.