James Taylor's half century turned the game Leicestershire's way as they eventually snatched a thrilling two-wicket win over Derbyshire on the penultimate ball of the match.
Set 151 to win at Grace Road, Taylor's 53 gave the Foxes the edge, especially after he his three sixes in four balls, and they just about held on to pinch victory at the death.
The Falcons registered 150 all out with just two balls left of their 20 overs, after Greg Smith had made 36 and Wayne Madsen 30.
Derbyshire had then looked favourites for the victory when left-arm spinner Chesney Hughes took career-best figures of 4-23 to help reduce the home side to 91-6 with only five overs to go.
But Taylor turned the game on its head by pulling Steffan Jones for a six over mid-wicket and then clearing the ropes twice more in the next over, bowled by Mark Turner.
The over brought the Foxes 19 runs, leaving them to score 18 off the final two overs for victory.
Taylor was caught at long-on off the bowling of Jones, ending his 31-ball innings, but Jacques Du Toit saw the Foxes home by hitting 22 off 15 balls, including three boundaries.
Leicestershire's fifth win in a row in the competition cemented their position in second place in the North group. They cannot be caught and will definitely have a home match in the quarter-finals.
Having won the toss, Leicestershire skipper Andrew McDonald decided to bowl first and Derbyshire were bowled out for 150 in 19.4 overs thanks to some accurate bowling and sharp fielding.
Abdul Razzaq, Harry Gurney and Jigar Naik claimed three wickets each as the Derbyshire batsmen struggled to gain any momentum.
Smith top-scored for them with 36 off 35 balls before being brilliantly caught and bowled by McDonald, but the Falcons then lost their last five wickets for 12 runs in the last three overs of their innings, with Razzaq taking 3-12, Gurney 3-34 and Naik 3-27.
The Foxes made a brisk start, reaching 37 in five overs before McDonald had a rare failure in the competition and chipped a catch to mid-wicket off Jones for 15.
His departure seemed to rock the home side's confidence as wickets fell steadily, before Taylor's brilliant innings swung the momentum back Leicestershire's way ahead of an exciting finish.