Mark Pettini's perfectly paced half-century helped Essex back to top spot and inflicted Somerset's fifth defeat in eight matches.
The opener contributed an unbeaten 60 to put his side well on course to overhaul their opponents' modest 150-7 at Taunton when bad light intervened with Essex 106-2.
After a short break, the visitors were given a revised target of 125 from 17 overs, which meant they needed 19 from 15 balls.
Ravi Bopara hit the first of them for four on his way to 33 not out and Essex breezed home by eight wickets with an over to spare. Jesse Ryder hit 28 at the top of the innings.
Leg-spinner Max Waller was Somerset's best bowler, with figures of 1-22 from four overs. But their seamers erred on the short side as Pettini and Bopara hit five fours apiece and Ryder four fours and a six.
With Hampshire losing to Surrey, victory was enough for Essex to overtake the previous leaders.
Adam Rouse struck an unbeaten 35 from 16 balls as Gloucestershire gained a thrilling three-wicket, final-ball victory against Kent at Bristol.
Wicketkeeper Rouse joined Gloucestershire on a month's trial last week and marked his second T20 game for the county with a brilliant innings, which included three fours off the last over of the game, bowled Australian international Doug Bollinger.
Gloucestershire looked to be out of contention when reduced to 101-6 in the 16th over, but Rouse received good support from Jack Taylor and Tom Smith to secure Gloucestershire's third win in the competition this season.
Twelve were required off the last over and Rouse got the job done with boundaries off the third, fourth and last balls.
Earlier, a sparkling 75 from Sam Northeast, which included five fours and four sixes, had dominated Kent's total of 150-6 on a slow Bristol pitch.
Jason Roy hit a breathtaking 63 from just 25 balls as Surrey galloped to an eight-wicket demolition of Hampshire, achieved with six overs to spare at the Kia Oval.
Kevin Pietersen, with 24 not out, and Gary Wilson, who hit an unbeaten 31, then provided the finishing touches to a great evening for Surrey against the southern group leaders.
Hampshire slumped to 57-6 before handy contributions down the order from Chris Wood (27) and Will Smith (25) saw the visitors post 131-9.
But it was clearly not enough, and Roy wasted no time tucking into the Hampshire bowling, sharing an opening stand of 78 in only 6.1 overs with Surrey's new overseas signing Tillakaratne Dilshan, who was forced to play second fiddle to his partner's pyrotechnics.
Sussex's hopes of squeezing into the knockout stages improved after an easy six-wicket win over Middlesex at Hove.
Middlesex were bowled out for just 107 off the penultimate ball of their innings and opener Chris Nash led the Sharks home with an unbeaten 74, hitting James Harris for a straight six to seal victory off the first ball of the 17th over.
After losing five successive games, Sussex have now won their last two and in the ultra-competitive South Division will still fancy their chances of a top-four finish.
With just one win so far, the Panthers are out of contention and there were few highlights for them in this performance, apart from Ryan Higgins' 31.
Sussex lost their talisman Luke Wright in the third over of their reply, leg before to Harris on the walk and, after a mix-up with Nash, Harry Finch was run out by Higgins' direct hit from the covers in the fifth over.
Like their visitors, Sussex were 40 for two at the end of the powerplay but Nash was in no mood to give it away and he eased to his first half-century of the season.
A stand of 44 in eight overs with Rory Hamilton-Brown (17) took the game away from Middlesex and Nash finished with 74 from 53 balls with three sixes and five fours.