Essex 153 for 6 (Zaidi 47) beat Hampshire 150 for 7 (Vince 62) by three runs
Ashar Zaidi starred with both the bat and the ball to boost Essex's hopes of a quarter-final place - as the visitors edged out Hampshire in a three run thriller.
Pakistani Zaidi helped Essex to a healthy 153 for six with a patient 47 before miserly figures of two for 16 halted Hampshire at the Ageas Bowl.
Essex are also top of Division Two of the Championship, leading Zaidi to say: ""It is amazing feeling winning four on the bounce and we are taking the momentum into the four day cricket."
Michael Carberry and James Vince, having been set 154 by Essex, took the chase steadily - knowing exactly what they needed and scored on and just above the required run rate.
Carberry looked more ready to open himself up, but it was his undoing when he slogged to cow corner, before Tom Alsop was caught and bowl for a duck by Dan Lawrence.
Spin slowed dried the runs up with Zaidi impressive, his first over going for just four and his second picking up Liam Dawson - who was driving to extra-cover.
But as Zaidi stocked up on dot balls, boundaries flowed off Vince's bat, on the back of another Test call-up. Vince reached his 19th Blast fifty from 37 balls, but the ball after Sean Ervine teed up to Tom Westley giving Zaidi a deserved second wicket.
Shahid Afridi spliced one back to Matthew Quinn and Vince finally departed as he was bowled by Graham Napier. But just as Hampshire looked set for a seventh defeat Lewis McManus provided a fightback with a four and massive maximum in the penultimate over to leave the hosts needing eight from six.
Wicket-keeper McManus was caught on the mid-wicket outfield from the second delivery, still seven needed but Ravi Bopara held his nerve - only going for two more runs.
Earlier having won the toss, Essex set off at a blistering start reaching 67 by the end of the power play, with every other ball seemingly rushing to the boundary off Jessie Ryder, Kishen Velani and Westley. But for all their heaving they lost Velani in the third over - chipping up to Vince at mid-off.
As easy as that catch was for captain Vince, his snaffle to see off Ryder, for 22, was unbelievable - as he gave international teammate Dawson his first of the night by diving full length once the ball had seemingly drifted over him. Dawson, who took three wickets on his England Twenty20 debut on the ground on Tuesday, grabbed the 50th 20-over wicket of his career when the booming Westley picked out Carberry on the point boundary.
That quick flurry of wickets and the introduction of spin quelled the run scoring as Zaidi and Ravi Bopara stutter - although the former did smash a six onto the concourse.
Zaidi accelerated from that bash, mainly scored on foot, to get within three runs of a third half century in a row but was the victim of a stunning direct hit from boundary rider Carberry and Bopara was caught at deep mid-wicket.
Ryan ten Doeschate hammered the final ball to Ervine on the long-on rope to set Hampshire 154 to win - which proved just enough.