Leicestershire 271 for 8 (Handscomb 103, van der Gugten 5-49) beat Glamorgan 262 (Ingram 68, Trevaskis 4-54) by nine runs
Australian international Peter Handscomb rescued Leicestershire from 59 for five with a superb 103 to set up a winning score against previously unbeaten Group B leaders Glamorgan and keep the defending champions in contention for the knock-out stages of the Metro Bank One-Day Cup.
Chasing 272 after seamer Timm van der Gugten had taken 5 for 49, Glamorgan were all out for 262, with Foxes left-arm spinner Liam Trevaskis their star man with the ball, taking 4 for 54 to go with the 47 he made with the bat in a vital 103-run partnership with Handscomb for Leicestershire's seventh wicket, although ex-Glamorgan man Roman Walker ran him close, taking the last three wickets for figures of 3 for 40 to seal a nine-run victory.
Veteran Colin Ingram top-scored for the Welsh side with 68. His dismissal to Trevaskis with 75 still needed from 55 balls looked to have swung the balance heavily towards the home side, but a List A career-best 61 from Dan Douthwaite took the contest into the penultimate over.
The result puts Lewis Hill's side on 10 points, one behind Glamorgan and Warwickshire - who also surrendered their unbeaten record against Yorkshire - and two ahead of Gloucestershire and Yorkshire.
Both Glamorgan, who take on Yorkshire in Cardiff in the final round of group matches on Wednesday, and Warwickshire, who face eliminated Nottinghamshire at Rugby School, are already sure of at least a quarter-final place. Leicestershire, who travel to Bristol to meet Gloucestershire, have the potential to finish in any of the top three places - or be knocked out on net run-rate.
The one shadow over their celebrations after this victory was an injury to Handscomb suffered while batting, after which he did not field in Glamorgan's innings and may make him a doubt for Bristol.
Needing to score at 5.44 per over, Glamorgan - missing top scorer Eddie Byrom through injury - lost both openers in first nine overs to all-rounder Ian Holland, Tom Bevan helping a leg-side delivery into the hands of short fine leg before Will Smale's attempt to clear the leg-side fence only picked out the man at deep square. They were 43 for 2 from 10.
Leicestershire's attack was depleted by injuries and Hundred call-ups, yet by the halfway stage of their innings at 108 for 4, they seemed not so much to be biding their time as making hard going of what was required.
They had lost Sam Northeast to a return catch tamely chipped back to Trevaskis for 31, the same score at which Kiran Carlson, showing signs of frustration, had holed out to deep midwicket off Tom Scriven. The rate needed was up to 6.56.
Billy Root was caught behind square on the reverse sweep off Trevaskis, Asa Tribe holing out to deep midwicket, a third wicket for the left-arm spinner. Ingram, who hit two sixes and seven fours, reached his fifty from 48 balls and needed to be there at the end if Glamorgan were to win, so little wonder there were loud celebrations among the home players when Trevaskis had him leg before sweeping.
Douthwaite's four fours and four sixes kept Glamorgan in the hunt but after Walker bowled Van der Gugten and had Andy Gorvin caught at backward point in the space of four deliveries, he was the hero again as Sol Budinger patiently waited for the ball to come down at deep midwicket and Douthwaite's brave effort came to an end.
Glamorgan had won the toss and while a frenetic opening powerplay saw them concede 59 runs after opting to bowl first on use on a green-tinged pitch but take four wickets, with a fifth quickly following in the 11th over. Four of them came from Van der Gugten.
The pacy Netherlands international dismissed Ian Holland leg before in his first over. Sent back by the lively Sol Budinger, skipper Hill was run out by Asa Tribe's direct hit from extra cover before the former edged to first slip, having hit six fours in a 23-ball 28.
The departure of the Foxes' leading run-scorer was quickly followed by that of their undoubted star turn, the Indian Test batter Ajinkya Rahane, who was leg before offering no shot, and Louis Kimber, who returned from The Hundred to be bowled through the gate for a four-ball duck.
New man Ben Cox hit six boundaries in his 34 but hooked Douthwaite to deep backward square, leaving the Foxes 105 for 6. The combination of Andy Gorvin and the spin of Carlson and Bevan proved restrictive but Handscomb and Trevaskis stayed patient, adding 103 in 23 overs before the latter was bowled by the returning Van der Gugten.
Handscomb pulled Gorvin for his only six and dispatched Van der Gugten for his 10th four before completing his second hundred of this year's competition, never hurried yet taking only 91 balls. He and Scriven added 47 in five overs before the Australian - limping towards the end of his innings - succumbed to a catch at backward point.