They had lost six wickets for 39 runs in 11 overs after being sent into bat.
They had made a Horlicks of a promising platform of 163-3 in the 34th over.
Enter Liam Plunkett.
The 30-year-old pace bowler is one of the cleanest strikers of a ball around.
In fact, Plunkett is one of the most powerful and athletic players in the country, the sort of chap who enjoys getting up at an ungodly hour of the morning to do all manner of devilish fitness work.
Plunkett’s forearms are as big as other people’s legs.
He is not so much a sportsman as a specimen.
If Yorkshire were to repair the damage and sellotape together that semi-final ticket, Plunkett the batsman had to produce.
In the space of 32 balls, he plundered 49 not out with three fours and three sixes – one of the maximums off pace bowler Jamie Porter soaring over long-on and crashing into the roof of a house at the Hayes Close end.
Through a combination of talent, judgment and prodigious power, Plunkett helped add 50 for the last-wicket with 17-year-old pace bowler Matthew Fisher, who contributed five.
Their efforts ensured Yorkshire had a competitive total to defend after all of 252-9 – if not quite the one in the region of 300 they had threatened to achieve.
Not content with shining with the bat, Plunkett then delivered in his primary role.
He took 3-58 from 10 overs of hostile pace bowling, snaring the key wickets of Tom Westley, Jesse Ryder and Ravi Bopara, to help reduce Essex from 95-1 in the 19th over to 129-5 in the 25th.
When captain Ryan ten Doeschate and wicketkeeper James Foster added 60 in 14 overs, the pendulum swung back to Essex once more.
But Will Rhodes removed both in a timely five-over spell, and Yorkshire held their nerve to win by 20 runs to set up a semi-final with Gloucestershire at Headingley on Sunday, September 6 with a 10.30 start time.
On paper, this was always a well-matched contest.
Essex have made Chelmsford something of a fortress in one-day cricket, while Yorkshire had five current England players on show – including Plunkett – and a sixth England man if you include Tim Bresnan.
One of that current England quintet was Adam Lyth, who had an Ashes series to forget with the bat, although he will forever treasure his part in the shared success of a series victory.
Lyth’s return to county duty began when he steered the first ball of the game to the third-man boundary off Reece Topley, the left-hander following-up by driving David Masters uppishly to the mid-off rope.
Lyth lost fellow opener Alex Lees with the score on 33 in the seventh over, the captain caught behind as he pushed forward at Topley.
Lyth had advanced to 36 when he was second out at 64, somewhat unluckily dragging a ball from Porter onto the stumps via his leg, a dismissal that summed up his recent fortunes.
Jonny Bairstow – another returning England man – looked in good touch on his way to 19, but was caught behind trying to force Ryder through the offside.
Yorkshire, in fact, perhaps went too hard at the ball at times on a slow pitch, and Jack Leaning struggled to get going in the early stages of his innings as Masters, in particular, posed problems.
Yorkshire should have fallen to 69-3 but Topley spilled a sitter when Leaning, on 10, picked him out at mid-wicket.
Topley put down another chance – albeit a tough low one – when Gary Ballance, on 22, turned Porter into the same area.
But after adding 67 with Leaning in 14 overs, Ballance fell for 32 when he was also caught behind trying to force through the offside off Bopara.
It started the dramatic collapse which continued when Rhodes clipped to deep square-leg and Adil Rashid was bowled swinging across the line.
Leaning skied to deep mid-wicket for the top score of 72, made from 99 balls, Bresnan falling to a catch in the same region before Steve Patterson was undone by a yorker.
Essex’s reply began poorly when Nick Browne drove firmly back to Bresnan, who inadvertently deflected the ball on to the stumps to run-out Mark Pettini.
Westley played some lovely strokes en route to a run-a-ball 54 before Plunkett rocked the hosts with his three-wicket burst.
While ten Doeschate remained, Yorkshire could never relax, but one ball after reaching his half-century, ten Doeschate drove Rhodes to Bresnan at long-on to fall for 52.
Bresnan completed the formalities with the wickets of Aron Nijjar and Topley to spark jubilant scenes among the visiting players.