James Benning's magnificent 189 not out failed to save Surrey from a two-run C&G Trophy defeat by Gloucestershire.
The hosts racked up 339-8 thanks to Ian Harvey's 108 and David Brown's 63 off only 26 balls, featuring five sixes.
Benning responded with four maximums and 28 fours to hit his first one-day century.
But he had no support until Neil Saker (22) put on 57 with him to take them to the brink of victory until Saker was run out off the penultimate ball.
The run riot began when Harvey hit his second century in this year's competition off 80 balls, hitting 15 fours until he was bizarrely run out.
He rejected a single and was dawdling outside the crease when the wicket-keeper threw down his stumps.
Brown, brought in for his senior debut, failed to score off his first four deliveries but then launched an astonishing assault.
Surrey's reply began badly, with Jonathan Batty and Mark Butcher falling to successive balls from Carl Greenidge but Benning changed the complexion of the game.
Such was the confidence he and Saker exuded, they went into the final over needing eight to win, which became three off two balls when Saker thrashed Greenidge over extra-cover.
But when Saker played the ball towards mid-wicket and set off for a single, Craig Spearman's throw was too accurate.