Karl Brown and Steven Croft put on an unbeaten century stand as Lancashire beat Essex by eight wickets in their in their Clydesdale Bank40 Group A match at Chelmsford.
The visitors passed their opponents' total of 186 all out with 21 deliveries to spare and, in doing so, booked a home tie in the semi-finals.
Croft made 66 and Brown 87 as they put on 160 in 30 overs to make sure the earlier efforts of Oliver Newby (5-35) with the ball were rewarded.
Essex had looked set for a much more formidable total as openers Tom Westley and Mark Pettini moved to 47 in the 10th over without looking in any trouble.
But Newby removed both in his first two overs and then put the home side firmly on the back foot at 70-3 when he also got rid of Greg Smith.
He later returned to remove Adam Wheater and Maurice Chambers as Essex batsmen failed to make the most of decent starts.
Five of them were dismissed in the 20s, among them Owais Shah who was the victim of a brilliant piece of work in the field by Brown, scoring a direct hit from deep extra cover which proved the highlight of fine fielding throughout the innings.
In their reply, the visitors did not get off to the best of starts as they lost openers Stephen Moore and Ashwell Prince cheaply.
But Croft and Brown were to regain the initiative with a dominant third-wicket partnership full of controlled aggression.
The pair scored freely against both pace and spin, while putting together Lancashire's highest third-wicket stand in limited-overs against Essex - beating the 114 between Clive Lloyd and Neil Fairbrother in 1986.
Brown's effort was his season's highest in all forms of cricket and contained eight fours and three sixes, while Croft struck five fours as Lancashire completed their sixth win in as many games in the competition with something to spare.