Tom Lammonby propelled Somerset into a handy lead on day four of the Bob Willis Trophy final, but Essex hold a potential trump card after edging the first-innings scores.
Lammonby raced along to 94 not out as the Taunton side moved to 159 for two – 123 ahead at tea – looking to reassert themselves on the game after ceding the advantage.
In the event of a draw on Sunday, Essex now know they will walk away with the trophy having secured the upper hand in any tie-break scenario by posting 337 for eight to Somerset's 301 all out.
With that in mind Somerset needed to make the running and 20-year-old Lammonby did just that in a highly accomplished knock that belied his youth and inexperience in just his sixth first-class outing.
Essex started the day on 271 for six, requiring another 31 runs to move in front.
When play got under way at 10.30am Somerset would still have fancied their chances of taking that advantage for themselves, but by 11am those hopes had vanished.
It was a slightly ill-disciplined start from the bowling attack, allowing 14 extras in that time to make it virtually impossible to build up early pressure. When Essex did achieve their target it came with four byes slipping through Steve Davies.
Lewis Gregory continued probing away, bowling Jamie Porter and dismissing Simon Harmer for a duck, to finishing with six for 72 before the innings reached its mandatory 120-over conclusion.
Ben Green and Lammonby safely negotiated seven overs in the lead up to lunch, before clearing the deficit in the afternoon.
Lammonby led the way as the pair reached 50 in the 17th over and 100 after 27.
Green was hanging in but Lammonby looked in wonderful form, standing up to Porter and Sam Cook with the new ball then getting the best of Harmer, the competition's leading wicket-taker.
His first 20 balls failed to yield a run but when Lammonby skipped down the track and lifted him for four the floodgates opened. Harmer's next batch of 20 balls included five boundaries and a six from Green.
Aaron Beard had the right-hander caught at slip for 41, with Porter removing Tom Abell for 15, but Lammonby continued his swift accumulation.
Twice he pumped Beard through cover off the back foot and hit a lovely straight drive as Harmer continued to struggle.
