After deciding to bowl first in Leicester, Somerset quickly had their hosts in trouble at 18-3. But from there, Leicestershire went on to dominate proceedings.
Wicketkeeper Ben Cox top scored with 89, while 60 from Nick Kelly and 77 from Ian Holland helped them to 289-8.
It was a chase that very soon proved out of reach for Somerset as they slumped to 48-5 and only some late hitting from number 10 JT Langridge with 32, got the total beyond three figures.
Alex Green claimed the final wicket of Jake Ball to end with 3-28 as they were all out for 125 in 30 overs as Leicestershire posted a huge 164-run win, which would be enough to take them top of Group A.
After winning three successive games to top the table, Lancashire bowled first but Northants raced to 347-6 in their 50 overs.
Opener Gus Miller struck 115, his first century in this format, while number three Aadi Sharma hit 61 and they put on 153 together before captain Nathan McSweeney scored 78 off 59 as they piled up the runs in Northampton.
Lancashire could not find that big partnership and when Marcus Harris fell for 57, the first of four wickets for India leg-spinner Yuzvendra Chahal, they were 180-5.
Teenager Joe Moores kept up the fight with 85 off 59 against a growing run-rate, but when he was run out after a mix-up with captain George Balderson, the game was up.
They were bowled out soon after for 280 in the 46th over as Northants claimed an ultimately convincing 67-run triumph.
Notts opted to bat at Beckenham and a maiden List-A century from opener Ben Martindale (101) set the platform for a strong innings.
When he was out, South Africa wicket-keeper Kyle Verreynne picked up the pace with 71 and some powerful hitting from Lyndon James (43) pushed the score to 293-9 in their allotted overs, while medium pacer Ekansh Singh produced best figures of 4-40.
In reply, Kent captain Daniel Bell-Drummond (44) provided early impetus but a third-wicket partnership of 115 between Sam Northeast, who hit 78 and Harry Finch put the home side in a strong position.
Finch went for 88 in the 45th over with 38 still required, but Chris Benjamin played the winning hand as he ended on 55 off only 34.
With 21 needed off two overs, he and Grant Stewart plundered 19 off James’ penultimate over and a five-wicket triumph was sealed with four balls to spare as Kent moved level on points with their opponents, Lancashire and Surrey in the chase for a top-three spot and a place in the knockout games.
Warwickshire and Gloucestershire had only won one game each at the halfway stage ahead of their meeting at Rugby School but it was the Bears who came out on top by six wickets.
Ollie Price hit a career-best 122 for the Glosters, as he shared strong stands of 90 with captain Cameron Bancroft (46) and 98 with Joseph Eckland (43).
But from 203-2, aided by two wickets in two balls from Jordan Thompson, they were hauled back in to 271-9.
Bears captain Rob Yates led from the front with the bat as he struck a List-A best 132 off 123 balls, including six sixes, to break the back of the target.
After a partnership of 147 with Vansh Jani for the third wicket, Yates fell, but Jani was there at the end on 66 with eight overs to spare.
