The Steelbacks suffered their third defeat in as many Vitality Blast matches as Lancashire Lightning eased to an eight-wicket win at Emirates Old Trafford.
Richard Levi made 40 for David Ripley's men, but Northants were never really in the hunt after posting a disappointing 123 for nine.
Levi was the only player to pass 17 for the Steelbacks as they slumped to a heavy reverse on Sunday afternoon.
Lancashire got home in just 16.1 overs as they boosted their North Group hopes, while Northants were left bottom of the embryonic standings.
The Steelbacks headed to Manchester having been beaten by Leicestershire Foxes and Notts Outlaws at the County Ground.
And things started well as Alex Wakely won the toss and Northants reached 62 for one - Ben Duckett was dismissed for 10 - after 5.5 overs.
But in the final ball of the powerplay, Jordan Clark clung on to a return catch blasted back at him by Levi and that began a spell in which the visitors lost three wickets for six runs in just 11 balls.
Josh Cobb and Richard Vasconcelos fell to fine catches by Arron Lilley and Keaton Jennings respectively.
And none of the other Steelbacks batsmen could dominate a Lancashire attack monopolised by slow bowlers.
Lancashire’s pursuit of their modest target began badly when Liam Livingstone was caught at the wicket off Seekkuge Prasanna for four.
But Lilley made a sprightly 23 off 14 balls before being caught by Levi at short third man off Graeme White.
The remainder of the innings belonged almost exclusively to Alex Davies and Jennings who steered their side home with an unbroken partnership of 88 for the third wicket in exactly 12 overs.
Davies was in particularly fine form, hitting three successive fours off White and reaching his fifty off 36 balls with half a dozen fours and one six.
Jennings is currently in fine form in all formats and supported his partner well by making 28 not out.
Lancashire Lightning: Livingstone (c), Davies, Lilley, Jennings, Vilas (wk), Clark, Croft, Faulkner, Parry, Parkinson, Lester.
Steelbacks: Levi, Duckett, Cobb, Wakely (c),Vasconcelos (wk), Crook, Prasanna, Kleinveldt, White, Sanderson, Hutton