Saif Zaib top-scored with a brilliant 92 from 58 balls as Northants posted what looked to be a testing 186 for seven in their innings, having been asked to bat by the hosts.
But it wasn’t enough as the Falcons got home with six wickets and an over to spare at 192 for four, with the Steelbacks bowling and fielding below par.
There was some brilliant power batting from Wayne Madsen and Shan Masood as the Falcons made it five wins on the spin to stay on course for the quarter-finals.
The win took Derbyshire above the Steelbacks into second in the table, with Northants dropping to third with three group games remaining.
Madsen and Masood smashed 95 from 50 balls to take the Falcons home.
Masood scored 57 from 43 balls and Madsen a destructive 73 with 10 fours and two sixes from only 37 balls as the Falcons cruised home against some ragged bowling.
Earlier, Zaib had revived the Steelbacks after key men Chris Lynn and Josh Cobb perished in the first four overs of the powerplay, along with Ben Curran.
Lynn skied a swing at Sam Conners and Madsen held a steepling catch at cover before Hayden Kerr removed Josh Cobb.
The Steelbacks skipper drove and pulled Conners for four consecutive fours but then lost his off stump making room to cut Kerr.
That followed Curran’s miscued clip at Mark Watts into the hands of mid on and at the end of six overs, the Steelbacks were 58 for three.
Rob Keogh was caught off a George Scrimshaw no ball but after hitting the free hit to the boundary, top edged a pull to third man.
Jimmy Neesham drove Conners over long off for the first six of the innings in the 10th over and Zaib added a second when he cut Scrimshaw over wide third man in the 12th.
Zaib mixed improvisation with placement to reach 50 off 36 balls but the introduction of Matt McKiernanan in the 15th over removed the dangerous Neesham who was stumped charging the leg spinner.
The Steelbacks plundered 22 from the 17th over when Zaib swept and drove McKiernan for two sixes but Scrimshaw and Watt conceded only10 off the next two.
Zaib pulled Kerr for his fourth six before he was run out but Lewis McManus drove the last ball for six to take his side to a competitive total.
The Falcons lost Luis Reece in the first over when he chipped a return catch to Cobb but Kerr pulled Tom Taylor for six and repeated the shot against Ben Sanderson as 16 came from the last over of the powerplay.
Kerr swung the first ball from Freddie Heidreich into the hands of deep midwicket but Masood took two boundaries from the wrist spinner’s next over to keep the Falcons on track.
Madsen drove and pulled Neesham for two fours to leave the Falcons needing 97 off the last 10 overs and he reverse swept Graeme White for six as 14 came from the 11th over.
The Steelbacks were struggling to contain the pair with Masood steering Sanderson to the third man boundary on his way to a 36 ball 50.
Cobb returned but Madsen ramped him for two fours as the Falcons accelerated towards their target with 46 coming from three overs.
A reverse swept six took Madsen to a 24 ball 50 and although Masood holed out to long on, only 36 were needed off the last five overs.
Madsen was caught behind off Neesham in the 19th over but the game was over as a contest and Leus du Plooy finished in style with a big six over deep midwicket.