Essex 212 for 9 (ten Doeschate 45, Harmer 44*, Dernbach 4-31) beat Surrey 210 (Foakes 77, Quinn 3-34, Bopara 3-46)
Tailender Simon Harmer hit an unbeaten 44 including the winning boundary to steer Essex to a thrilling one-wicket win over Surrey in a low-scoring Royal London Cup clash at the Kia Oval.
Harmer, who has five Test caps for South Africa to his name, saw his side over the line in the final over to inflict a second defeat on Surrey - last season's beaten finalists.
In pursuit of 211 at an attractive asking rate of 4.22 an over, Essex lost their top three inside seven overs. Nick Browne wafted outside off against Sam Curran to be caught by a tumbling Ben Foakes, Alastair Cook was pinned on the back foot by a Sam Curran off-cutter to go lbw, then Varun Chopra feathered to slip against Jade Dernbach to make it 12 for 3.
Under leaden skies and with the floodlights on, the visitors regathered composure through Tom Westley and Ravi Bopara in a stand of 66 that ended when Westley top edged a Dernbach bouncer to midwicket.
Bopara undid his good early work by driving without moving his feet against Dernbach to gift Foakes another catch, while Adam Wheater chopped on against Ravi Rampaul to leave Surrey scenting victory.
With 83 still needed, Ashar Zaidi suffered a rush of blood to the head by dancing down the pitch against Gareth Batty only to chip to mid-off but visiting skipper Ryan ten Doeschate showed all his experience to add a crucial 51 before edging a leg-glance against Batty into the gloves of Foakes.
Harmer and Neil Wagner came together with 32 required, a deficit they halved before Dernbach, with another fierce, throat-high bouncer, bagged his fourth wicket to have Wagner caught on the hook at deep square.
With four required off Sam Curran's final over, Harmer sealed it by sweeping a low full-toss for four to backward square with four balls to spare. Harmer finishing unbeaten on 44, his best in List A cricket as Essex landed their second win in as many starts.
After being invited to bat, Surrey had been indebted to Foakes for an unbeaten 77 - the only half-century of the match - that helped post a modest 210 after the hosts were dismissed with 14 balls of their allocation still to be bowled.
Guilty of losing wickets at regular intervals and generally to rash strokes, Foakes showed his middle order how it should be done during an assured 140-minute stay.
He came to the middle with his side in a pickle. Mark Stoneman lent back in aiming a back-foot force against Matthew Quinn only to pick out Chopra at point. With the south-east London venue also playing host to an international wine-tasting challenge, hopes of a vintage display by Kumar Sangakkara were soon 'corked' when the Sri Lanka ace prodded, almost involuntarily, at a Wagner lifter and feathered a catch through to keeper Wheater.
Essex skipper ten Doeschate introduced offspinner Harmer at the Pavilion End to enjoy immediate rewards. Advancing in defence to an arm ball, Dominic Sibley pushed inside the line to be stumped then, five runs later, Rory Burns rushed down the pitch aiming to drive only to see the ball turn past his outside edge and peg back off stump to make it 46 for 4.
Surrey's fifth-wicket partners Scott Borthwick and Foakes dug in to add 73 until Borthwick's good fortune ran out. Having previously top-edged short of the keeper and chipped close to long-on, the left-hander dragged on against Bopara to depart for 37.
Bopara's next delivery ran across left-hander Sam Curran who followed and edged behind for Wheater to pull off a stunning low catch in his left glove.
Foakes, stylish and untroubled throughout, reached his 50 from 69 balls and with four boundaries, went on to add 57 for the seventh wicket before Tom Curran nicked an attempted pull against Matthew through to the keeper.
Wagner picked up two more late wickets in having Batty and Dernbach held at long-on, while Bopara nipped out a third by bowling Rampaul as Surrey limped past 200.