Essex 186 for 4 (Bopara 70*, ten Doeschate 55*) beat Surrey 167 (Clark 60, Porter 4-38) by 19 runs
An unbroken stand of 117 in 10.4 overs between Ravi Bopara and Ryan ten Doeschate was enough to keep Essex's hopes of qualification alive at The Oval and dumped Surrey out at the group stage for the fourth time in five years.
On a two-paced pitch, Essex had started sluggishly, and at 87 for 4 after 12 overs dominated by Surrey's spinners, were set for little more than a par score. But ten Doeschate's expert rotation of the strike, followed by a late blitz from Bopara after a characteristically slow start took them to an imposing 186, which proved too many for Surrey's faltering batting line-up.
For Essex, the qualification picture is not as simple as they might hope. Their game against Kent tomorrow night is a must-win, but even that might not be enough; their net run-rate is comfortably the worst of the sides still in contention, and they could well find themselves needing winless Glamorgan to pull off an upset against Hampshire to seal a quarter-final spot.
Essex lost three early wickets as their top order struggled to time the ball early on, and Surrey's veteran spin duo of Gareth Batty and Imran Tahir looked set to keep them tied down. Batty's figures - 1 for 15 in four overs - were by no means flattering, with his subtle variations and guile resulting in a boundary-free spell.
When ten Doeschate reached his fifty with a boundary and a single at the start of the 17th over, Bopara was on 21; they ended unbeaten on 55 and 70 respectively, as Bopara took advantage of some profligate death bowling from Jade Dernbach and Sam Curran for three fours and four sixes in the final three overs to take him from 21 off 18 to 70 from 35.
From the England perspective, it must have smarted to see Curran with the white ball in his hand, not least given the Australians' game at Derby had seen the two touring seamers yet to play a game - Mitchell Starc and Michael Neser - share six wickets earlier in the day.
Curran's final over - the 19th - included three full tosses, two towering sixes, and went for 22 runs all told, and while regular Blast games represent the only real cricket on offer to him, they can hardly be considered ideal preparation for a young man on an England Test contract ahead of a possible Ashes bow later in the series.
Since playing in the Test against Ireland, Curran has been limited to seven Blast games and the first two days of a Championship match, meaning that both Neser and Starc have bowled more red-ball overs than him in that time. We are more than used to hearing complaints from touring teams about a lack of quality match practice during long tours; it should rankle that England's domestic set-up means the same is true for them when they play at home.
With the bat, things were little better for Curran. He has been a useful, free-scoring No. 3 for them this season, with 222 runs and a strike-rate of 144.16 before this evening, but chewed up four dot balls against Mohammad Amir, before chipping a couple of boundaries over long-off and then holing out for a run-a-ball eight, as Bopara took an excellent catch running back at square leg.
His time will come back around - failure is a much more regular a feature in T20 than success - but this night did not belong to him.
Surrey have struggled throughout the season to score runs regularly, with only Aaron Finch ending the tournament with more than 350 runs, and so it proved again here.
Jamie Porter - who was only playing due to a last-minute injury to Aaron Beard during Essex's warm-up - took three Powerplay wickets in his first appearance of the season to remove Finch - well held by the diving Simon Harmer at mid-off - then Curran and Mark Stoneman with successive balls to seemingly end the game as a contest in the fourth over.
Will Jacks and Ollie Pope threatened to salvage the chase, both smiting sixes into a sell-out crowd, but wickets fell all too regularly for Surrey to seriously threaten to pull off a win.
Jordan Clark did his best to keep things alive with a 32-ball 60, but found himself needing to hit 31 off Porter's final over. He hit four then six from the first two balls, but Porter held his nerve to close out the win, firing in two yorkers before clinging onto a steepling caught-and-bowled chance.
Matt Roller is an assistant editor at ESPNcricinfo. He tweets at @mroller98