Richard Levi marked his return with an important innings as the Steelbacks ended Leicestershire's 100 per cent start in this season's NatWest T20 Blast.
The big-hitting South African batsman, who had been ruled out since May due to concussion, hit 41 from 28 as the Steelbacks racked up 165 for eight after losing the toss.
Rob Keogh (37) and Alex Wakely (34) also provided crucial contributions to kick-start Northants, who were 68 for four in the 10th over.
And though Leicestershire got off to a good start in their reply, the Steelbacks pulled it back thanks to wickets from Ben Sanderson, Rory Kleinveldt and Keogh.
When the rain came, after 14.3 overs of the Leicestershire innings, the Steelbacks were two runs ahead on the Duckworth-Lewis method.
And that meant David Ripley's men could claim two points ahead of the televised clash with Nottinghamshire Outlaws at Trent Bridge on Saturday afternoon.
The Steelbacks had lost the toss and were put into bat at Grace Road, with all eyes on Levi as he looked to get his side off to a fast start.
He did that, taking 11 runs from the first over, but Northants soon lost a wicket as Adam Rossington hooked one and was caught on the boundary off Mathew Pillans for six.
Levi was up and running though, picking off fours down to fine leg with ease to ensure the Steelbacks had the sort of run rate they wanted early on.
But Josh Cobb couldn't follow in Levi's footsteps when it came to finding the boundary and the former Leicestershire man was caught behind off Gavin Griffiths for just seven.
The Steelbacks finished the powerplay on 40 for two and it was the start the in-form Foxes would have hoped for.
Levi did his best to keep his team ticking over, smashing a six and adding a few more fours to the tally, but Ben Duckett was soon stumped by Luke Ronchi off Callum Parkinson for 10.
And Levi soon followed Duckett back into the away dressing room as he was caught by Dieter Klein off the bowling of Griffiths for 41.
The Steelbacks were 72 for four at the halfway stage and, the men in the middle, Wakely and Keogh, knew they had plenty of work to do.
The 100 finally came up with six overs to go, but Leicestershire were still by far the happier team at that point.
Wakely and Keogh then started to step on the accelerator though, with both cashing in for the County.
The Steelbacks took 21 runs from a huge 17th over, but Pillans was to bowl Keogh from the final ball of it to leave the away side 143 for five with 18 deliveries remaining.
Steven Crook announced his arrival with a six and a four as the total started to become competitive, but Leicestershire pulled it back well in the final two overs.
Pillans bowled Wakely for 34 before Crook was caught on the boundary in the final over and Kleinveldt was then dismissed by Klein with two balls remaining.
It was the final flourish the Foxes wanted, leaving the Steelbacks on 165 for eight at the end of their innings.
Leicestershire started their reply in composed fashion before Sanderson eventually forced the breakthrough, having Ronchi caught for 13 by Duckett.
The Foxes were 49 for one at the end of the powerplay, with the Steelbacks turning to the spin of Tabraiz Shamsi and all-action Keogh.
And it was the latter who got the next wicket as he bowled Cameron Delport for 30, prompting cries of 'Keogh, Keogh, Keogh' from the travelling Steelbacks supporters.
Mark Cosgrove then looked like he would take control for the Foxes but he was eventually bowled by a delighted Kleinveldt for 41 from 25 balls.
The Steelbacks started to tighten things up and when rain stopped play, Leicestershire were 107 for three, needing 59 runs from the final 5.3 overs.
And, to the delight of the vocal Steelbacks supporters, who were stationed next to the bar, there was no more play, meaning the away side could celebrate a hugely welcome win.
Leicestershire Foxes: Ronchi (wk), Delport, Cosgrove, Ackermann (c), Pettini, Hill, Wells, Pillans, Parkinson, Klein, Griffiths.
Steelbacks: Levi, Duckett, Cobb, Rossington (wk), Wakely (c), Keogh, Crook, Kleinveldt, Shamsi, Sanderson, Gleeson.