Essex 341 for 6 (Bopara 89, ten Doeschate 89) beat Hampshire 230 (Rossouw 93, Coles 4-48, Bopara 3-39) by 111 runs
Ravi Bopara produced an all-round extravaganza to condemn Hampshire to their first defeat in this season's Royal London One Day Cup while also giving Essex Eagles hope of reaching the knockout stage.
Former England star Bopara smashed an almost flawless 89 with the bat before he celebrated figures of 3 for 39 with his medium pacers. Bopara had put on 150 with Ryan ten Doeschate, who also scored 89, to send Essex to a good total of 341 for six.
Former Hampshire fast bowler Matt Coles also chipped in with four wickets, a best for Essex, as Hampshire lost wickets at regular intervals, despite Rilee Rossouw's high quality 93 - with Essex prevailing by 111 runs.
Essex, who had only tasted victory once in their opening three fixtures, won the toss and elected to bat on a belting wicket under heavy clouds, having lost the last three matches deciding to bowl first.
Debutant Rishi Patel added 60 for the first wicket with Alastair Cook. Patel, who scored a record-equalling five centuries for the Second XI last season, aggressively reached a quick-fire 35 before he and Cook departed within two overs of each other. Cook, who has only managed to average 20 in this format this season, edged Brad Wheal behind, Patel picked out Wheal at long on and then Dan Lawrence was bowled by Liam Dawson.
A below-par score looked on for Essex when Tom Westley tickled a delivery that rose on him behind to hand James Fuller his maiden Hampshire wicket - and left the hosts on 147 for 4.
But Bopara and ten Doeschate joined together in the 29th over to rebuild and accelerate. Both reached half centuries, Bopara from 57 ball and ten Doeschate off 39 deliveries, including seven boundaries.
The century stand came up in 81 balls but Bopara was given a life, the ball after dispatching Kyle Abbott into the River Can, when Mason Crane downed a chance at deep point.
The partnership reached 150, an Essex high for the fifth wicket against Hampshire, but without another run being added Bopara departed for 89 when he heaved Abbott to Sam Northeast at deep square leg.
Paul Walter arrived at the crease and clobbered a maximum off his first balled faced, before ten Doeschate tanked Fuller over the ropes three balls later. Ten Doeschate fell for 89, having passed 6,000 List A runs, when he was run out by Crane but Walter crashed another six to end on 22 from 14 balls as Essex reached a par 341 for 6.
Hampshire's reply started slowly as they lost both openers and Sam Northeast within the first 13 overs.
Peter Siddle had Tom Alsop lbw while swinging across the line before Aiden Markram skied to Jamie Porter at mid-on and ex-Kent skipper Northeast handed keeper Robbie White a steepling catch, the latter two to Coles, leaving Hampshire 37 for 3.
Vince and Rossouw guided Hampshire back on track with a 77-run stand for the fourth wicket, but they couldn't catch up with the required run-rate. Vince, on the back of a career-best 190 against Gloucestershire on Friday, eased through the gears and reached 47 before slog sweeping Lawrence to Walter at cow corner.
Dawson fell soon after when he slashed Bopara to point, but Rossouw continued his swashbuckling innings with a six into the pavilion.
Rossouw and new man Gareth Berg gave Hampshire hope again with a useful 79-run partnership but the latter steered to short third man before Fuller was bowled by Bopara.
Rossouw departed when he chased a ball down leg side to top edge to short leg before the result was secured when Abbott scythed to Porter at third man, for a record-equalling four catches in an innings for an outfielder for Essex, and Wheal was bowled.