Sussex 287 for 9 (Beer 75, Evans 68) beat Essex 283 for 7 (Westley 61, Lawrence 54) by one wicket
Will Beer brilliantly shattered his best score for Sussex to hand his side a nervy one-wicket victory with one ball to spare in their Royal London One Day Cup match against Essex.
Leg-spinner Beer arrived at the crease on 94 for 6 before he produced a superb 75 in a three-figure stand with Laurie Evans. Beer's previous best was an unbeaten 45 against Durham in 2014 as he helped the Sharks on their way to an incredible win.
The gutsy victory was secured when No.10 and No.11, Danny Briggs and Mir Hamza, scored the required seven off the last over to send Sussex to their fourth victory in five outings.
Essex won the toss and elected to bat on the same pitch on which they beat Hampshire on two days earlier.
Alastair Cook and Varun Chopra, who returned from a quad injury, put on Essex's best opening stand in the competition so far as they reached 73 without loss.
Chopra was given a life on 15 when he was dropped at first slip by Phil Salt but failed to scored a third successive format century when he was lbw to a huge George Garton in-swinger.
Cook chopped onto his stumps four balls later before Tom Westley and Dan Lawrence set Essex about their total. Both were forced to be patient in their quest to find runs, firstly against a moving ball and then on a slow pitch.
Other than a well-struck six straight down the ground, Lawrence appeared particularly risk averse as he reached his fourth fifty of the competition from 69 balls, shortly after Westley passed the milestone off 54 deliveries.
Essex's second mini-blip saw Westley caught on the heave to third man, having put on 104 with Lawrence, and then Ravi Bopara edged behind 13 balls later. Lawrence fell between 50 and 60 for a fourth time in an enigmatic season when he departed in an almost identical manner to Westley on 54.
Ryan ten Doeschate (35), Robbie White (21) and Matt Coles (16) chipped in to take the hosts to 283 for 7 - as David Wiese ended up as the pick of the Sharks bowlers with 3 for 54.
In reply, Jamie Porter struck in his third over as he used the new ball to his advantage when he jagged a delivery into Salt's middle stump.
Former England all-rounder Luke Wright passed 5,000 List A runs when he reached 25 but only scored another five runs before chipping to Chopra at short extra cover and Garton was castled by Bopara for 38.
Coles, who took four wickets on his first appearance of the season against Hampshire, then entered to dismantle the Sussex middle-order.
Harry Finch mistimed to Chopra in the covers before the former Kent man took the wickets of Wiese and Ben Brown in consecutive balls.
Both Wiese and Brown were tempted to tickle at the ball outside the off stump to edge to Middlesex loanee Robbie White - leaving Sussex 94 for 6, having lost four wickets in 15 balls.
Evans and Beer resuscitate the innings with a century stand off 126 balls. The record partnership for the seventh wicket for Sussex against Essex ended on 121 when Evans, having reached a half-century in 55-balls, steered to Coles at short fine leg off ten Doeschate.
Beer, who had passed fifty for the first time in one-day cricket from 79-balls, continued his destruction with two maximums, but played one shot too many as he picked out Coles at cow corner.
Abidine Sakande was run out by Porter but Hamza and Briggs held their nerves with a 24-run stand for the final wicket to secure an epic victory.