Timm van der Gugten’s 3-20 reduced the Essex reply to 27-3 but opener Adam Rossington (41) and the excellent Paul Walter (53) lit the blue touchpaper on their innings with an 83 partnership.
However, both fell quickly, Rossington going to Marnus Labuschagne (3-26) and Mason Crane conceded just two from the 16th over to leave Essex with too much to do as they stumbled to 156 all out.
Gloucestershire chased down Somerset’s total of 194 to stay in the hunt for the knockout stages in a thrilling finish in Taunton.
Tom Banton carried his bat for 77 and Ben Green hit his best T20 score of 47 off 25 balls as the home side posted a daunting target.
The visitors conceded 32 off the final over with Josh Shaw removed from the attack midway through the over after bowling two no-balls over waist height.
Gloucestershire kept the scoreboard ticking in the chase as Miles Hammond (42), James Bracey (31), Beau Webster (39) and Jack Taylor (27) all made valuable contributions.
They still needed 13 off the last over, only for Ollie Price and Ben Charlesworth to hit a six apiece off Green’s bowling to win it with one ball left.
Rain reduced play at The Oval to 10 overs each and South Group leaders Surrey wasted no time, running up 103-5 with Laurie Evans scoring 25 off 13 balls and Kent bowler Grant Stewart conceding 19 off the final over.
Another rain interruption lopped two overs off the Kent reply, meaning they needed 87 off eight.
They got off to a poor start as England paceman Reece Topley had Daniel Bell-Drummond caught by Ben Geddes off the second ball.
Feroze Khushi hit 35 off 19 balls and with 17 needed off the last over, Chris Jordan conceded just 11 as Kent fell five runs short.
