It was the second win in the space of three days for David Ripley's men, who have rekindled their hopes of qualifying for the quarter-finals having claimed just one point from their first six fixtures.
They had lost their previous four home games, but were too good for Lancashire, who were reduced to 130 for seven by an excellent all-round bowling performance.
The Steebacks then batted sensibly against some quality bowling, particularly from the fiery pace of Luke Wood, to ease home at 131 for three with 10 balls to spare.
With the ball, Wayne Parnell claimed two for 28 and there were wickets for Ben Sanderson, Brandon Glover and Graeme White - his 100th in T20 cricket - while Mohammad Nabi bowled beautifully to concede just 18 runs from his four overs, with Tom Taylor conceding just 11 from two.
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After losing the toss, Steelbacks made a good start with the ball.
There was frustration in the second over as Vasconcelos dropped a chance at slip off the bowling of Sanderson, with Finn Allen the lucky batsman.
Former England man Keaton Jennings wasn't so fortunate in the next over as Vasconcelos this time held on to take a good catch at short mid-wicket to leave the visitors 11 for one.
Allen then hit a six and a four off consecutive balls, but just when it looked like that dropped catch might prove costly, Sanderson's slower ball caught the Kiwi out and he was bowled middle stump for 16 to make it 23 for two.
Davies got a life as Nabi almost clung on to what would have been a stunning caught and bowled, but the Lancashire man survived.
The 10th over proved to be an excellent one for the Steelbacks, as first Davies luck run out as he was caught at mid-off by Parnell. miscuing an attempted hit over the top from Glover's first ball of the match.
Rob Jones walked to the crease and quickly walked back again as he was run-out by a superb direct hit from the fine-leg boundary by Taylor, the Lancashire batter was undone going for a second leg bye.
At the halfway point, Lancashire were 64 for four and struggling.
Every time the visitors looked to be getting some momentum, they lost a wicket and it happened again in the 13th over as they slumped to 81 for five.
Dane Vilas this time sliced a White delivery to Sanderson at deep cover, the pace bowler making up a lot of ground before diving forward to snaffle the ball.
Lightning were struggling to hit boundaries as the Steelbacks continued to keep things tight, with Nabi particularly miserly as his four overs went for just 18 runs.
Lancashire brought up the 100 in the 17th over as Danny Lamb reverse swept White for a rare four, but they went into the final three overs of their innings on 105 for five and needing some fireworks.
Lamb knew it and immediately hammered Parnell for a big six over square-leg, but was out the next ball, miss-hitting to Taylor at mid-off and he was gone for 20 off 12 balls.
And with him went Lancashire's chance of any sort of acceleration, with Seven Croft struggling for any sort of timing as he ended up 33 not out off 37 balls as Lancashire posted 130 for seven.
Lightning needed to produce something special with the ball, and Saqib Mahmood's opening over was a real tester for Vasconcelos, who eventually got off the mark with a cover drive for four off the fifth ball.
Things went pretty smoothly for Northants until the fourth over when Mahmood struck to make it 21 for one, Rossington driving him to extra cover where Jones took a sharp head high catch.
The pace of Mahmood and Luke Wood was causing the Steelbacks batters problems, and in the fifth over Vasconcelos was hit on the helmet by the latter, the ball flying away for four leg byes.
The left-handed opener responded by hitting the first two balls of the next over for four, and the Steelbacks ended the powerplay in good shape at 43 for one.
The introduction of spin from both ends saw the Steelbacks chip away with singles, and with a requited rate of around 6.5 per over that was okay.
The re-introduction of a bit of pace from Lamb led to Parnell hitting the first bundary for four overs, as the Steelbacks reached the halfway stage well set on 68 for one
Vasconcelos perished soon after though, caught on the deep square-leg boundary for 41 off the left-arm spin of Tom Hartley to make it 70 for two.
It was quickly 77 for three as Parnell, who had played well for 25 from 24 balls, played on to his off stump trying to guide a Wood delivery down to third man.
With 12 overs gone, the Steelbacks suddenly had something to think about as they still needed 54 to win at almost seven an over.
Step forward Nabi to ease the pressure as he hit three fours in one Mahmood over to see his side to 91 for three.
Lightning needed wickets, and quickly, but they weren't forthcoming.
The Steelbacks, with Nabi in control, chipped away at their target without taking any risks, before a straight six from Keogh had the job all but done at 127 for three.
The Steelbacks stalwart then finished the job off Mahmood in the 19th over, much to the delight of the home supporters inside Wantage Road.
They had waited a long time for this!!