The second semi-final at Edgbaston on Saturday sees a north v south clash with the chance for one county to claim their first-ever spot in the final of the Vitality Blast.
Essex Eagles will take on Derbyshire Falcons from 14:30 BST with the winner taking on Nottinghamshire Outlaws or Worcestershire Rapids.
Essex Eagles
Road to the Final - P14 W5 L4 T1 NR4
Essex's place at Finals Day looks all-the-more remarkable when you look at their record.
The Eagles won just two of their first ten games in the Blast this year and won just five overall, but pipped Kent Spitfires and Somerset to the final quarter-final spot in the South Group.
Their opening win came in their second game. Cameron Delport bludgeoned 129 from 49 balls including seven fours and 14 maximums and Tom Lawrence's unbeaten 57 took Essex to a mammoth 226-4.
They claimed a 52-run win, but they would only manage one win in the next 34 days.
That victory came against Gloucestershire in early August. Surpassing 200 once again after 77 not out from Ryan Higgins, they claimed a 25-run victory.
Their other opening eight games resulted in four losses and four abandoned games, leaving them well off the pace until their four-game charge started on August 22 against Sussex Sharks.
Mohammad Amir's four wickets ripped through Sussex, who went on to top the South Group, with Lawrence's 59 not out and Ravi Bopara's 24-ball cameo of 45 doing the damage.
A thrilling tie against Hampshire came next with Lawrence (69) in the runs once again, whilst Bopara'a 117-run stand with Ryan ten Doeschate led Essex to victory against Surrey in the penultimate game.
Bopara had hit form at the right time with his 70 off 35 against Surrey and it was his unbeaten 47 that saw Essex over the line and into the quarter-finals as they scored 189 to beat Kent with Delport smashing 64 from just 29.
Derbyshire Falcons
Road to the Final - P14 W7 L5 NR2
It was a similar story for Dominic Cork and his Derbyshire Falcons, who won just one of their opening five games before finishing the campaign with three wins to secure a quarter-final spot.
Chasing 164 to beat Yorkshire Vikings in their opener was more than a good start for the Falcons, but their next four saw them lose to Birmingham Bears, Nottinghamshire and Worcestershire in comfortable fashion, compounded by a washout against Lancashire Lightning.
Poor form turned to inconsistency in August. They completed the double over Northants, lost to Durham Jets, then scored 207 against Yorkshire Vikings en route to victory before they were all out for 94 just two games later.
Their innings of 200 was the evidence this team had promise. No real world-class stars, yet Wayne Madsen was performing well for the Falcons as he does year-in-year-out whilst Leus du Plooy also got in on the action.
But like Essex, they peaked late and timed their charge perfectly. Three wins in four days catapulted them towards the quarter-finals. They started off by bowling Northamptonshire Steelbacks out for just 100 and knocking them off for just one wicket and the bowlers stepped up again against Leicestershire Foxes, restricting them to just 128 and winning by nine wickets for the second match running.
The clincher was a shock. They travelled to runaway leaders Lancashire and it was Madsen who top-scored with 69 from just 38 balls, whilst Billy Godleman's 57 proved crucial.
Their key weapon with the ball Ravi Rampaul did the rest and it was his three wickets earned Derbyshire a place in the quarter-final.
The Final Eight
Lancashire Lightning v Essex Eagles
Lancashire had run away with the North Group. Leading from day one, Liam Livingstone and co. had been by far the best side in the group, if not competition, but there's no substitute for momentum...
Bopara, ten Doeschate and Delport were once again the lynchpins for Essex's success.
Alex Davies' 55-ball 80 was all that Lancashire had to offer. Dane Vilas' 41 set Essex 160 for victory.
44 from Delport at the top of the order coming from 30 balls, slow by his standards, was followed by 45 from ten Doeschate and 39 from Bopara as the pair sharing another match-winning stand of 60 and booked their place at Finals Day with a six-wicket win.
Gloucestershire v Derbyshire
Derbyshire went into this one, like they do most games, as underdogs. Gloucestershire had Michael KIinger, one of the best batsmen of recent times in the Blast, second only to Chris Gayle in all-time T20 centuries.
The Falcons' underrated bowling attack were at it again. Restricting Gloucester to 135-7 they were always in control, and it showed with the bat.
Madsen was the glue of the innings once again for Derbyshire, who raced out to 55-2 inside six overs. Madsen's sidekick du Plooy abetted him once again as the pair added 72 and guided Derbyshire to Finals Day courtesy of a seven-wicket win.
For these two it may well be a case of whoever handles the occasion better will succeed. Both are flying after their ends to the campaign, Essex have the names and the power, but Derbyshire have the nouse and a brilliant coach who knows what it takes to win the competition.