At Derby, Ben Geddes posted 109, Max Holden contributed 65 as part of a 156-run third-wicket stand with the captain and Zafar Gohar took 3-35 as Middlesex beat Derbyshire to secure a place in the knockout stage.
Joe Cracknell also reached 44 not out to set a target of 328 to win, which would have been Derbyshire’s highest-ever successful chase in the format.
Caleb Jewell top-scored with 54 but Derbyshire, who went out of the competition with a loss to Yorkshire on Friday, slumped from 82-1 to 240 all out.
Middlesex host bottom side Sussex in their final match of the group on Tuesday, while Derbyshire now cannot finish higher than sixth.
Durham sit third thanks to a 20-run win over Essex at Darlington, overcoming the absence of Emilio Gay through a shoulder injury the opener suffered during their defeat to Middlesex on Friday.
With the match reduced to 38 overs because of rain, Colin Ackermann was 80 not out and Ben Stokes hit 43 off 27 – including consecutive sixes – as Durham reached 229-5.
Noah Thain gave Essex hope with 76 to put his total in this season’s competition beyond 500 runs, but his side’s campaign will now end with their home game against Yorkshire.
Third-placed Durham travel to Worcestershire, who are four points behind them with a significant run rate inferiority, in their decider.
Hampshire hammered 383-9, their second-best score in List A cricket, to beat Sussex with the help of six consecutive sixes at Hove from Toby Albert, who hit 86 off 37 balls but was eclipsed by 18-year-old Ben Mayes’ 109 from 115 deliveries.
Former Sussex player Ali Orr added 105 as part of a 51-run win, marking the visitors’ best total since they recorded 396-5 at Kent in 2022.
Charlie Tear responded with 111 runs off 94 balls but Sussex have lost all but one of their matches in this season’s competition.
Fourth-placed Hampshire will start their match against Derbyshire four points behind Durham and Yorkshire.
Reigning champions Worcestershire will be on the brink of elimination when they host Durham after a last-ditch defeat against Glamorgan at Cardiff.
Captain Jake Libby hit a fourth century in as many innings with a sparkling 105 as Worcestershire posted 278-9, with Henry Cullen hitting seven fours – one fewer than Libby – on his way to 77.
In reply, Callum Rhys Nicholls (70), Jack Hope-Bell (58) and Timm van der Gugten (45) led Glamorgan’s charge and Andy Gorvin hit four off the final ball as the home side won by two wickets.
Worcestershire must win and significantly improve their run rate to go through in their final group game. Glamorgan have played their final match and will finish eighth.
Tuesday, 11 August (11:00 BST)
Group A
Gloucestershire v Northamptonshire (Cheltenham)
Somerset v Lancashire (Taunton)
Surrey v Nottinghamshire (The Oval)
Warwickshire v Kent (Rugby)
Group B
Essex v Yorkshire (Chelmsford)
Hampshire v Derbyshire (Southampton)
Middlesex v Sussex (Radlett)
Worcestershire v Durham (Worcester)