Chasing 149 to win, the Steelbacks got home with nine balls to spare as Tom Sole and Graeme White got them over the line with nine balls to spare.
Ben Duckett earlier made 33 off 24 balls, including an audacious scoop for six off pace bowler Zak Chappell, after Ben Curran had caught the eye.
Curran celebrated the two-year contract he was awarded earlier this week with a bright 29 off just 18 balls, taking four boundaries in an over off Chappell.
His striking in a 50-run partnership with Duckett was key in the Steelbacks racing to 63 for one in the powerplay, giving themselves a platform they did not waste.
Josh Cobb made a run-a-ball 30 and, after a wobble in which four wickets fell in three overs, White finished the job with 21 off nine deliveries.
White won the match by clubbing Colin Ackermann’s off-spin for six over deep midwicket as off-spinner Sole kept his composure on his T20 debut at the other end.
It was only a second win in this year's Blast for the Steelbacks and makes no difference to their finishing position at the bottom of the North Group.
But it at least provided some satisfaction after the Foxes denied them in a remarkable game at the County Ground at the start of the competition, when the Steelbacks failed to defend 213 for three.
Having put the Foxes in, the Steelbacks made a fine start with the ball, reducing the home side to 35 for three in the powerplay.
Northants had been forced to change their plans in the second over when a distraught Gareth Wade had to be removed from the attack on his T20 debut after two of his first three deliveries slipped out as beamers.
Cobb had to bowl the five balls remaining in the over yet it was the Foxes who were soon in disarray, losing Eckersley, Harry Swindells and Ackermann inside the first six overs.
Wade made himself feel a little better by taking a catch at mid-off when Swindells hit Luke Procter over his head.
A smart piece of work by Duckett behind the stumps saw Chappell depart as he swung at a wide delivery after Wakely had introduced White’s left-arm spin, leaving the Foxes 37 for four in the seventh.
It came down to 21-year-old Harry Dearden to rescue the Foxes’ innings, at least in part, sharing a stand of 62 with Ateeq Javid for the fifth wicket on the way to a 40-ball 61 that included a couple of sixes and five fours.
Dearden might have added a few more but for bowler Richard Gleeson’s quick thinking, the bowler running him out in his follow-through as he tried to steal a single from a miscued shot by Lewis Hall that landed halfway down the pitch.
Aadil Ali was also run out as the Foxes finished on 148 for seven, and it wasn't enough as the Steelbacks sealed a morale-boosting success.