Gloucestershire 184 for 7 (Taylor 50, Charleswoth 47*) beat Essex 171 (Shaw 3-29) by 13 runs
Jack Taylor's second fifty in three matches made it three wins in a row for Gloucestershire to spark hopes of retaining the Men's Vitality Blast.
Gloucestershire had begun their defence with five straight defeats but victories over Kent Spitfires, Hampshire Hawks and now Essex have given hope they can sneak back to finals day via the back door.
Captain Taylor had dragged his side to a par score of 184 with 50, to go with Ben Charlesworth's 47 not out, before Josh Shaw's three for 29 made sure the Eagles fell 13 runs short.
The 2019 champions Essex remain winless, with their only points coming from a wash-out. They can now only get a maximum of 22 points with fourth placed Glamorgan already on 20 points.
For the third home match in a row, Simon Harmer chose to bowl first but it was Gloucestershire who edged the powerplay.
They managed 58 runs, par for the first six overs at the Ambassador Cruise Line Ground, but lost Miles Hammond just about caught at slip by a juggling Paul Walter and Cam Bancroft attempting back-to-back sixes.
But Essex demonstrably won the middle overs by holding the visitors to just four boundaries from the end of the seventh over to the start of the 16th.
Darcy Short failing to kick on from reaching 33 and Ollie Price barbequing himself didn't help their cause, but tight bowling closed off their scoring options.
Taylor's hard running dragged Gloucestershire back into the innings before his hard-hitting got them closer to a defendable score.
Firstly, he took Matt Critchley for three fours in an over and then he carted Luc Benkenstein for two huge sixes - one of which smashed a press box window.
It helped the Gloucestershire skipper reach his seventh T20 fifty in 34 balls.
A wicket in each of the last three overs kept the away side to 184, with Mohammad Amir taking two of them to return three for 33, while Charlesworth's useful 31-ball cameo left him unbeaten on 47.
In the two previous games at Chelmsford, Essex had been set targets of 221 and 220 and it had quickly been apparent the chase would be above them.
On this occasion, they stayed in the fight despite losing regular wickets. Michael Pepper and Jordan Cox each went big then got out in the powerplay, while Dean Elgar suffered a tortured nine balls in a half-hour spell in the middle.
Paul Walter threatened to be the man to put Essex in complete control with a spritely 39 but he and Benkenstein fell in the same Charlesworth over leaving the hosts needing 82 in eight overs.
Critchley and Charlie Allison clubbed 21 and 17 off the 14th and 15th overs, but then Critchley was bowled by Shaw as the momentum swung like a Newton's cradle.
But Harmer clothed to point, Allison holed out, Noah Thain picked on long on, and Amir was run out as the game fell out of Essex's grasp as Gloucestershire squeezed at the death.
