After choosing to bat, Yorkshire were bowled out for 50 in glorious sunshine, their lowest total for 45 years.
In blameless conditions, apart from the usual nip and nibble at this time of year, they were blown away in just 18.4 overs half-an-hour before the lunch break.
Essex, 10-2 at the interval as 12 wickets fell in the opening session, scored 142 in reply, their innings ending five balls after tea had been delayed with nine wickets down.
Then, as if to put what had gone before into perverse perspective, Yorkshire ended a madcap day on 161-2 in their second innings, a lead of 69, Harry Brook top-scoring with 57 not out, his maiden first-class fifty, and Jonny Bairstow striking a momentum-changing 50, the balance of power, incredibly, now resting with the visitors.
“It was an interesting day, wasn’t it?” said Bairstow. “If you were thinking about coming on Monday you should probably have come (yesterday). It was a bit difficult to sum up, to be honest.
“There was obviously plenty in the pitch, and Essex bowled well, and every time there was something on offer, we either nicked it or missed it.
“For us to fight back and bowl them out cheaply showed where we’re at, and we’re in a good position now with batting still to come.
“I just tried to play as positively as possible, and Harry Brook played a really good innings.”
Yorkshire’s first innings total was their lowest score since they were dismissed for 43 in their second innings by Surrey at the Oval in 1973.
It was their lowest first innings total since they were bowled out for 40 by Kent at Bradford in 1967.
Although Yorkshire’s batting has been a problem for some time this was a curious capitulation considering their strength.
But Joe Root bagged a golden duck, Bairstow hit seven and Cheteshwar Pujara made nine as Sam Cook took 5-28 from nine overs and Peter Siddle 4-7 from 3.4, with only captain Gary Ballance (22) reaching double figures.
Yorkshire even picked seven specialist batsmen after deciding to leave out a frontline spinner.
Jack Leaning, the No 7, was batting after only 40 minutes as Yorkshire collapsed to 22-5, with only Bairstow “got out” in the sense that he received a fine ball from Cook that nipped away and tipped back off stump.
Otherwise Brook nibbled to second slip, Adam Lyth was caught behind driving outside off stump, Root drove at a full, straight delivery and edged to first slip, and Pujara went lbw, working across the line.
Cook maintained a probing line from the River End, but it was never a 50 all-out pitch/conditions.
The innings continued ingloriously as Leaning was lbw on the walk, Tim Bresnan lbw pushing forward, Steve Patterson caught behind nibbling, Jack Brooks taken at third slip, feeling for a drive, and Ballance brilliantly held at third slip by Nick Browne, having pushed at the ball away from his body.
One thing Yorkshire do not lack, however, is fighting spirit, and they certainly do not lack for quality bowlers.
Bresnan, Coad and Brooks each took three wickets in a gutsy fightback, and Patterson one wicket on his return from a broken finger, as Essex failed to make the most of an excellent platform.
The hosts also played some profligate shots. Alastair Cook drove loosely and was caught behind, Tom Westley drove expansively and got an inside edge that took out middle and, when Browne was bowled pushing forward, Essex were 12-3 just after lunch.
They had rallied to 58 when Ravi Bopara edged to first slip, Dan Lawrence scoring a fine 48 from 77 balls with seven boundaries before Bresnan pinned him in an excellent spell from the Hayes Close end, leaving the home side 72-5.
Wickets continued to tumble as James Foster was bowled through the gate, Ryan ten Doeschate lbw propping forward, Siddle caught at mid-off, Porter lbw and Simon Harmer caught at mid-on after striking a useful 36 from 60 balls.
At that stage talk around the ground was of the last time that a Championship game had finished inside a day (for the record, it was Kent versus Worcestershire at Tunbridge Wells in 1960), but Yorkshire were in no mood to implode for a second time.
Promoted to open, Bairstow changed the mood with some blistering strokes, his positive approach visibly rocking the bowlers.
Cook was dispatched dismissively over long-off for six as Bairstow reached a splendid 42-ball half-century before Siddle bowled him driving off an inside-edge, the bowler following up with an unnecessary send-off.
Lyth chipped in with 27 before edging Siddle to a juggling Harmer at second slip, although it looked as though the ball might not have carried.
Brook and Pujara added an unbroken 65 to cap an outstanding Yorkshire fightback.