Faheem Ashraf saw the Steelbacks home with two balls to spare as David Ripley's men beat Birmingham Bears by four wickets on a golden afternoon at Edgbaston.
It kept Northants' slim hopes alive of qualifying for the Vitality T20 Blast quarter-finals as they moved off the bottom of the group and up to sixth.
The Steelbacks began the day having to win their last three matches to reach the top four of the North Group and were cruising in a chase of 151 at 128 for two in the 15th over.
But wickets began to tumble and five runs were needed from the final five balls.
Ashraf then guided Henry Brookes wide of third man for two before striking the winning boundary over extra-cover.
Birmingham Bears had chosen to bat on a used wicket but slumped to 109 for five in the 17th over only for Will Rhodes, with 45 in 31 balls, and Chris Green, with 23 from 13 to boost them to 150 for six, taking 20 runs from the final seven balls of the innings.
Before then, the Steelbacks spinners had a grip on the innings with turn available.
Rob Keogh spun one sharply past Matt Lamb’s inside edge to bowl him for just one and deceived Adam Hose to have him stumped for 24.
Left-arm spinner Graeme White also earned a stumping when Dom Sibley advanced and missed an off-drive to fall for 24 in 20 balls.
Rhodes kept the Bears together - twice slog-sweeping to the short leg-side fence - and the blast from Green in the final over, hitting three fours off Ben Sanderson, gave the home side something to defend.
The Northants chase was given a bright start by Richard Levi, who made a timely return to form in making 44 from 27 balls - his highest score in the competition this season.
He took three fours from Oliver Hannon-Dalby’s opening over before dealing with Jeetan Patel’s off-spin by twice sweeping him for four.
Levi eventually fell trying to hit Rhodes over mid-off but he laid the platform for the pursuit at 73 for two in the eighth over.
Captain Josh Cobb then shared a stand of 55 in seven overs that appeared to have put the game to bed, Cobb striking two sixes into the Raglan Stand.
But trying to repeat the shot he holed out to deep midwicket for 42 from 36 balls.
And when Dwaine Pretorius’ measured 26 from 24 balls was ended by a superb low return catch by Patel, work was left for the Northants middle order.
The task appeared straightforward with 16 needed from 18 balls but Alex Wakely and Rob Keogh couldn’t find the boundaries that would have killed the game.
One reserve-sweep from Wakely earned four past backward point but Keogh was bowled swinging at Green’s final delivery and Wakely then fell to a Brookes nip-backer first ball of the final over.
Suddenly the Bears sensed a chance and Tom Sole would have run himself out taking a run straight to mid-on had Lamb’s throw struck.
Ashraf, with four needed from four, then took over to win the game.
Birmingham Bears: Sibley, Hain, Hose, Rhodes, Lamb, Burgess (wk), Green, Thomson, Brookes, Patel (c), Hannon-Dalby.
Steelbacks: Levi, Rossington (wk), Cobb (c), Wakely, Pretorius, Keogh, Ashraf, Sole, White, Sanderson, Muzarabani.