Hampshire 134 for 3 (Vince 87*) beat Essex 133 (Westley 44, Crane 3-24, Dawson 2-31) by seven wickets
Mason Crane and Liam Dawson spun Hampshire towards victory before James Vince took them over the winning line with a thunderous 87 not out to give the visitors their first victory at the Cloudfm County Ground in Chelmsford for five years.
Spin twins Crane and Dawson ripped through Essex Eagles' batting in the middle overs as they snatched figures of 5 for 55 from their combined eight overs to set up a seven-wicket thrashing.
The Eagles, having been 81 for 1 at one point, lost nine wickets for 52 runs in 47 balls, to fall well below par.
Hampshire knocked off the 134 required inside 14 overs, with captain Vince raising his bat for his second fifty of the competition, to condemn Essex to a single win from their opening five fixtures.
Hampshire, who have now won two Vitality Blast matches on the bounce after ending their Somerset hoodoo last week, hadn't previously won on this ground in any competition since a T20 victory here in 2014 - with this being only their 10th success at Chelmsford this century.
Vince won the toss, stuck Essex in, and was immediately high-fiving Chris Wood and Dawson after Cameron Delport edged the first ball of the match to first slip.
Adam Wheater and Tom Westley, who had been promoted to the top of the order then enjoyed a boundary-hitting contest. Westley won the battle with three huge sixes and a trio of boundaries to Wheater's four inventive fours and sole maximum in the pair's 81-run stand in 53 balls.
But Dawson and Crane entered the attack and dismissed Westley and Wheater in successive overs before ripping through the rest of the Eagles' batting.
Crane then suckered Ryan ten Doeschate into a hoof down the ground, Chris Morris snaffling at long-off, before Dan Lawrence was bowled next ball.
Shane Snater was run out by Wood attempting a foolhardy second run and then Simon Harmer chipped to Sam Northeast at short cover, Dawson and Crane ending with middle-order figures of 2 for 32 and 3 for 24 respectively.
Overseas duo Adam Zampa and Mohammad Amir quickly followed as Essex lost eight wickets for 32 runs in an epic 40 ball collapse.
Paul Walter then thumped 26 off 13 balls to give the hosts some respectability but Matt Quinn was castled to leave him stranded - the Eagles all out for 133.
Aneurin Donald scored four and out in two balls before Vince and Rilee Rossouw comfortably ticked through the runs in a 78-run stand. Vince, who opened his campaign with 50 against Kent, tonked one over long-on to accompany a series of gorgeous fours to reach his milestone in 34 balls. Rossouw slapped to the straight boundary to depart for 25 but Vince continued to take his tally to three sixes and 12 fours.
He ended unbeaten on 87 as he and Northeast eased Hampshire towards the line with a 50 stand. The latter was bowled but Vince scored the winning runs two balls later.