Essex 207 for 8 (Westley 71) beat Gloucestershire 204 (Scott 64, Taylor 62, Snater 4-48) by two wickets
Tom Westley's patient innings of 71 led Essex Eagles to a thrilling two-wicket Royal London Cup victory over Gloucestershire at the Bristol County Ground.
In reply, the Eagles made 207 for 8, reaching their target off the last ball of the game. Aron Nijjar saw them home with a rapid 32 not out after Westley had laid the foundation with his 90-ball innings.
Needing two to win off the final delivery from Jared Warner, Snater cut a short ball past backward point for four.
Gloucestershire's early slump was much of their own doing, having reached 46 for 1 following the early loss of skipper Chris Dent for a duck.
Tom Lace fell to a decent delivery, Ryan ten Doeschate's first of the game, which nipped back and pinned him leg before for 19.
But James Bracey was then run out in a mix-up with Ben Charlesworth, who clipped the ball to mid-wicket and called for a quick single. Charlesworth appeared unsettled by the incident and, having played well to reach 22, offered a tame catch to point off Harmer.
Then Graeme van Buuren failed to commit fully to a lofted drive and was caught and bowled by ten Doeschate.
Taylor and Scott had no option but to build steadily, taking the score to 98 for 5 after 30 overs. Taylor was first to his half-century, off 71 balls, with four fours and a six. The pair had added 99 when he was caught aiming a big shot to leg off Nijar.
Scott's fifty occupied 75 deliveries, with five fours. He celebrated with a six over mid-wicket off Snater.
But the 49th over from the same bowler saw Matt Taylor caught at long-off, Scott edge to short third and Josh Shaw taken at mid-off before Ben Allison ended the innings.
Essex lost Alastair Cook with the score on 14, bowled behind his legs by Matt Taylor before left-arm spinner Tom Smith began to make inroads, getting the ball to grip from the Pavilion End.
He bowled Will Buttleman with a delivery that straightened and had Michael Pepper well caught by the diving Charlesworth, who had just been posted as a second slip.
Westley moved to a sound fifty, made from 65 balls, with five fours, and found a reliable partner in 20-year-old Josh Rymell. Playing his first List A innings, the youngster moved to 30 before being bowled attempting to sweep a full delivery from van Buuren with the total on 120.
The experienced ten Doeschate could make only five before lofting a catch to long off to give van Buuren his second wicket and Adam Wheater quickly fell lbw to Taylor.
Harmer was stumped advancing to van Buuren before Westley was controversially run out, a bail apparently already dislodged before wicketkeeper Bracey broke the stumps.
It didn't matter because Nijar came in to smack two sixes and two fours, turning the game in the final overs.