Sussex were cruising to victory. Chasing a paltry 146, a rollicking start kept them firmly on course for an easy two points.
When Tom Alsop fell for a splendid 82 at the end of the 13th over, Sussex were 119-4, needing 27 to win from the last six overs.
But what followed was a period of manic batting in which eight wickets fell for just 23 runs, handing the visitors an unimaginable comeback victory at Hove.
Gloucestershire headed out to bat after Ravi Bopara won the toss and opted to field first. Both teams were unchanged from their previous encounters.
Sussex started strongly, with Harrison Ward bagging a wicket first ball as Miles Hammond found Bopara at mid-off.
Obed McCoy got the dangerous James Bracey, who nicked one to the keeper. Steven Finn compounded the misery for Gloucestershire, accounting for Ian Cockbain.
At the end of the powerplay, Gloucs were a 33-3. Delray Rawlins and Archie Lenham bowled well on a pitch where the ball kept low occasionally.
Rawlins fired his darts with accuracy, getting rid of Ryan Higgins who top-edged to Alsop, while Lenham found some turn. The visitors were floundering at 49-4 at the halfway stage.
Glenn Phillips found his mojo with three hits to the off-side boundary as Lenham lost control over his length. Rawlins kept things tight and bowled an impressive spell of 1-13, with 11 dot balls.
Phillips tore into McCoy, racing to his half-century with some strong back-foot play, a feature throughout his innings of 66.
Captain Jack Taylor rode his luck with some streaky boundaries but took on Tymal Mills and Finn, with Finn bowling a costly 19th over. His wayward slower balls travelling to all parts.
The pick of the shots was Taylor’s majestic lofted extra-cover drive for four off the last ball as the over went for 16.
McCoy made Phillips drag one on – and Taylor was run out by Tim Seifert as he tried to sneak in a single as the Windies bowler varied his pace beautifully, conceding just three runs off the final over.
Gloucestershire having finished on 145-6, the run chase was rocky to begin with, David Payne getting the new ball to nip back, dismissing Seifert LBW in the first over.
The Tom Alsop show began with a massive six over long-on. He attacked Josh Shaw, using his crease to put the bowler off and pouncing on some error-strewn bowling.
A mis-timed shot from Bopara was safely pouched by Higgins running in from deep. The spinners found some assistance, while Benny Howell was content with bowling his cutters to a tight wicket-to-wicket line and a packed leg-side field.
Fynn Hudson-Prentice and Alsop rotated the strike, not willing to take much risk as the required rate was a tad over seven.
Alsop brought up his fifty and then cut loose, feasting on Zak Chappell feeding him width. Jack Taylor’s loopy leg-breaks were treated with disdain from Alsop, who went big leg-side for four and a couple of sixes, the second one a result of Phillips’s feet touching the boundary at long-on while he tried to throw the ball back to Hammond.
Both Hudson-Prentice and Alsop were stumped in the next over bowled by former Sussex player Tom Smith. Alsop was eventually dismissed for 82.
At that point in the match, Sussex needed 27 from just 36 with six wickets in hand. But then, calamity struck.
Cricket induces strange happenings – and this was yet another inexplicable exhibition of the sport’s see-saw nature.
Harrison Ward got a feather on Chappell’s bouncer and Phillips had Oli Carter caught behind attempting a cut.
Still, 18 were needed off the final four with Mills and Rawlins in the middle. But the panic button was spammed, and the slide became irreversible when both Mills and Rawlins returned to the pavilion following some poor shot selection, both succumbing to top-edges.
The following two overs yielded just six runs, as Gloucestershire now sensed the opportunity to strike back when it mattered most.
Chappell bowled a fine penultimate over as Finn and Lenham failed to find the boundary.
Sussex were bowled out for 141 with three balls to spare, Finn the last to be dismissed by Payne. The gleeful Gloucestershire players were cock-a-hoop, beating the team home in front of a packed Hove County Ground by four runs. David Payne now leads the Vitality Blast wickets chart with 17.
This funny old game is never short of the twists and turns it has to offer and while Sussex will hope to get such collapses out of their system early, they still need to win at least five games from the remaining six to book a Finals Day berth.
They next face Essex at Chelmsford the coming Friday (17 June). Gloucestershire host Glamorgan next Saturday.
