Derbyshire booked their place in the T20 Blast knock-out phase for only the third time with an 11-run win over Lancashire in the North Group.
Half-centuries from Wayne Madsen and Billy Godleman set a 163-run target that the Red Rose were unable to chase down, despite Liam Livingstone’s 58.
Sussex can also celebrate a knock-out stage spot in the South Group, after a seven-wicket win over Glamorgan.
Alex Carey’s 61 and Laurie Evans’s 45 reeled in the target in 17 overs.
Shaun Marsh and Colin Ingram both made half-centuries for Glamorgan in Cardiff, but their tally was not enough in the event.
Derbyshire starts key with bat and ball
Old Trafford was heaving for some Bank Holiday Monday cricket in the searing sunshine, and Lancashire and Derbyshire did not disappoint in a thriller.
In their final game of the group stages, Derbyshire knew a win was enough to put them through and despite losing Matt Critchley early on at Old Trafford, the arrival of Madsen at the crease to join skipper Billy Godleman kick-started their innings.
The veteran took control, thrashing a Liam Hurt free-hit for a maximum and swept away a Matt Parkinson turner for another big boundary.
He reached his 50 in 27 balls and made a further 19 before he departed with Derbyshire on 129-2, and Godleman also carved out a half-century before he left on 57 at 134-3 an over later.
Despite some tight bowling towards the back-end of the innings, Derbyshire made an above par 162-3 and set Lancashire a decent target to chase.
The response started disastrously, as Alex Davies holed out to Anuj Dal for a second-ball duck from Logan van Beek’s delivery.
Wayne Madsen caught Steven Croft’s big heave and Ravi Rampaul, who had been bludgeoned for a couple of fours just a few balls previous, got a key wicket.
Rampaul then blew out Josh Bohannan’s middle stump for his 20th T20 wicket of the season to leave Lancs wallowing on 39-3.
Liam Livingstone gave the Red Rose hope with some clean, powerful hitting before he left on 58, and Keaton Jennings was also unseated two balls later.
Glenn Maxwell dragged onto his own stumps with the score at 108-6, leaving the hosts shorn of their majors batting powers with five overs to go and Derbyshire cruised through to the quarter-finals.
Sussex race to victory and move into quarters
Nick Webb, BBC Wales
Sussex’s Australian keeper-batsman Alex Carey smashed 61 off 30 balls to steer them to a seven-wicket win and a home quarter-final.
The visitors romped home with 3.1 overs to spare despite a hand injury preventing captain Luke Wright from batting.
Carey gave them enough impetus to cruise home with David Wiese smashing a huge six high into the Cathedral Road stand in his 45 not out.
In-form Andrew Salter took 3 for 37 in an inexperienced Glamorgan attack.
Earlier Glamorgan’s 174 for four was one of their better batting performances of a struggling season, with Colin Ingram striking 50 off 30 balls to follow Nick Selman’s 40 off 23, while Shaun Marsh top-scored with a solid 52.
The medium pace of David Wiese helped limit the charge with 1-30 in his four overs, and Sussex made light of their target to record their 8th win.
Derbyshire await the knock-out stages in early September having completed their programmes but there are still games left this week.
Lancashire play Leicestershire on Friday in their bid to finish top, when Sussex host Gloucestershire and Glamorgan welcome Hampshire.
The next games are Durham against Birmingham on Tuesday which is now academic in terms of their quarter-final hopes, and Somerset go to Surrey.