Leicestershire 253 for 9 (Swindells 75, Lilley 41, Steel 4-33) beat Surrey 225 (Clarke 82, Patel 52, Mike 3-34) by one run (DLS method)
Leicestershire pulled off a dramatic one-run victory after Surrey lost three wickets in the final over of a rain-affected Royal London Cup match that had seemed to be theirs for the taking.
Veteran Rikki Clarke appeared to have steered an inexperienced Surrey into a share of the Group One lead with Glamorgan and Somerset when he hit a six off the final ball of the penultimate over as they chased a revised target of 227 from 39 overs, leaving them four to win from the final six deliveries with three wickets in hand.
But in an extraordinary climax, Clarke - who should have been run out twice in that last but one over - was leg before to Ben Mike for 82 with five balls left before Dan Moriarty was run out and Matthew Dunn bowled from consecutive deliveries, giving Leicestershire the spoils with one ball to spare.
Earlier, former Durham leg spinner Cameron Steel took 4 for 33 on his Surrey debut, conceding no boundaries in his 10 overs as Leicestershire, having been put in, made 253 for 9 from 50, including a List A-best 75 by opener Harry Swindells, 41 from Arron Lilley and 33 from Ed Barnes.
Already deprived of 11 players because of The Hundred and with three in the England Test squad, Surrey were without two more experienced players in Hashim Amla, who has a groin injury, and Mark Stoneman, left out after feeling ill.
But after Ryan Patel's 52 off 33 balls had put them in the driving seat, Leicestershire's bowlers bounced back with seven wickets in the last 11 overs, Mike finishing with 3 for 34, 16-year-old leg spinner Rehan Ahmed 2 for 25 and Barnes 2 for 34.
Swindells had done a fine job in the anchor role for the Foxes, hitting five fours to go with an early six over midwicket off Dunn, holding the innings together for 36 overs before top-edging Steel to short fine leg.
Rishi Patel fell into a trap when he was caught on the hook for 20, but apart from Lilley's 28-ball blitz as the second wicket put on 57 in 53 balls, there was no substantial support for Swindells and it was only through the late industry of Barnes, who made 33 from 36 balls largely in singles, that the Foxes' total limped past 250 with two many batsmen giving their wickets away carelessly.
Steel - who dismissed Lewis Hill, George Rhodes and Lewis Kimber as well as Swindells - should have had a maiden five-for but spilled a low return catch offered by Mike.
Ahmed bowled his leg spin beautifully, quickly trapping Patel leg before after the opener had hit eight fours and two sixes in a 27-ball half-century that saw him dropped on the midwicket boundary by Lilley on 48. Steel had been caught at midwicket without scoring.
Ben Geddes was stumped going down the track to off-spinner Rhodes, and Surrey began to wobble after Jamie Smith - captain in Amla's absence - was caught at deep midwicket for 34 and Nico Reifer and Tim David were both caught behind.
The drama gathered pace in the penultimate over, which began with Surrey needing 13 from 12 balls, when Clarke should have been run out twice by bowler Gavin Griffiths and McKerr was caught at deep midwicket before Clarke slammed the last ball over Griffiths' head for six - but the best was still to come.
