Essex slipped to a three-wicket defeat at Old Trafford after Lancashire chased down 253 to win on the final day from the penultimate ball.
After rain delayed the start of play following a weather-affected third day, Essex declared on their overnight total of 203-3.
That initially left Lancashire needing 253 from 51 overs, but after another delay - this time for bad light - they had 47 overs to get their total.
And they got there with just one ball to spare after a dramatic finale where three quick wickets fell before Wayne White scrambled the winning run after being dropped by Saj Mahmood.
Jaik Mickleburgh was left 53 not out by the overnight declaration, while Mark Pettini had also made an unbeaten 36.
The home side quickly lost openers Paul Horton and Luke Procter in their run chase, but Karl Brown and Ashwell Prince both made 80 to give them the necessary impetus.
But Reece Topley took five wickets to give Essex hope of holding out - or even grabbing an unlikely win themselves.
However, they were unable to prevent Lancashire from grabbing the winning runs from the penultimate ball.
