Ravi Bopara struck a superb unbeaten 39 to take Essex into a fifth Vitality Blast Finals Day after a six wicket win over Lancashire at Durham.
Former England all-rounder Bopara hit four sixes in a stunning 18-ball knock as they chased down 160 with four balls to spare in a thrilling quarter-final at Emirates Riverside after Lancashire had to move their home fixture due to a clash with the fourth Ashes Test at Old Trafford.
Bopara also claimed two wickets, but his key contribution came when he smashed two of the three sixes that came off Liam Livingstone's leg-spin in the penultimate over to reduce the target from 23 off two overs to one off one.
He shared an unbroken 60 in five overs for the fifth wicket with Ryan Ten Doeschate, who top-scored with 45 off 31 deliveries.
Lancashire opener Alex Davies top-scored with an unbeaten 80 off 55 balls in Lancashire's 159 for five, sharing a fourth-wicket partnership of 89 in 11 overs with captain Dane Vilas (41).
The Lightning were forced into a rebuilding job after the departures of Livingstone, Steven Croft and Australian Glenn Maxwell inside the first seven overs, leaving them at 47 for three.
Livingstone was bowled having a heave at Aaron Beard five balls into the match before Bopara had Croft caught at deep mid-wicket with his first ball and Maxwell went lbw.
Davies and Vilas then ran Essex ragged with twos aplenty into the gaps.
For the visitors, this fixture could hardly have been further from Chelmsford on two counts - distance and dimensions of the playing area.
Lancashire had requested the boundaries to be pushed right out to suit their plethora of pace-off options with the ball, and Vilas hit the only six of the innings when he pulled Cameron Delport's medium pacers over deep square-leg from the last ball of the 16th over.
New-ball seamer Beard struck twice, Bopara (two for 28 from four overs) and captain Simon Harmer (nought for 13 from three) were the pick of the Essex bowlers.
Tom Westley hit two boundaries off Croft in the first over of the chase before offering a simple caught-and-bowled chance to Saqib Mahmood's third ball in the second over to leave Essex nine for one.
Rain delayed proceedings for 29 minutes, meaning no loss of overs, at 14 for one after 3.1 overs.
Delport then hit three fours off James Faulkner in the sixth to help Essex to a healthy 49 for one.
But, when trying to clear deep mid-wicket off Maxwell's off-spinners at the start of the ninth over, he holed out to Croft running around from long-on for 44.
Then, next ball, Adam Wheater was run out going for two by a direct hit from Josh Bohannon running in from deep square-leg.
Ten Doeschate and Dan Lawrence, Essex's leading Blast run-scorer this season, took the sting out of the situation with a partnership of 39 built in identical fashion to that of Davies and Vilas earlier.
But the latter was brilliantly caught at long-off by a diving Faulkner off Livingstone's leg-spin in the 15th over as the Eagles slipped to 105 for four, needing 55 more.
The target then became 35 off three overs with Ten Doeschate and Bopara together.
Bopara hit Faulkner for six over long-off, tipped over the boundary by a diving Croft, to take the target to 23 off two, before continuing his assault to secure a Finals Day berth at Edgbaston on September 21.