Josh Cobb cracked a career-best 103, but the Steelbacks' Vitality Blast misery continued at the hands of Birmingham Bears.
On a sun-soaked Sunday afternoon at the County Ground, the home side failed to chase down the opposition's 187 for seven, having lost the toss and been forced to bowl first.
Cobb did his best to inspire a run chase, smashing the first T20 century by a Steelbacks player at Northampton.
But it could not provide a first Blast win of the season for the Steelbacks as Cobb got no support from the other end and his team lost by 17 runs.
With Richard Levi failing a late fitness test, the Steelbacks, who continue to do without injury victims such as Adam Rossington and Rob Keogh, lacked enough firepower to win it.
Bears skipper Grant Elliott took three for 43 and Jeetan Patel two for 17 from his four overs to ensure the away side wrapped up their fourth victory in 10 T20 games this season.
The Steelbacks, who have now lost nine of their 10 matches, were made to pay for a poor final seven overs with the ball as the Bears took 92 runs from that period.
Chris Woakes did most of the damage, finishing unbeaten on 57 to overshadow Ian Bell's earlier 43.
Seekkuge Prasanna (2-33) and Nathan Buck (2-35) both grabbed two wickets, but the Bears got up to a challenging total.
And it was too much for the Steelbacks, despite Cobb's brilliant solo batting effort.
After winning the toss, the Bears suffered an early blow as Richard Gleeson kept the batsmen on their toes and eventually forced a mistake from Ed Pollock. The opener departed for just one as he skied one to Prasanna, who took the catch.
It was a fine opening over from Gleeson as his pace posed constant problems for the opposition and allowed them just five runs.
Bell, who had smashed a stunning 131 from just 62 balls in the reverse fixture at Edgbaston in July, then started to get into the groove, notching a couple of boundaries.
Buck nearly got rid of Adam Hose, who was fortunate to see a nick fly between wicketkeeper and first slip.
But Hose did go from the final ball of the over as he tried to scoop the ball over Ben Duckett but only managed to find the gloves of the wicketkeeper, departing for eight.
It was to be a strong powerplay period for the Steelbacks, who limited the opposition to 38 for two.
The Bears continued to tick along until taking 19 from one Ben Sanderson over, prompting the Steelbacks to turn to the spin of Prasanna.
And the Sri Lankan eventually struck, having Sam Hain caught by Brett Hutton at long on for 31.
Another wicket followed soon after as key man Bell, who had looked good for his 43, was caught by Prasanna to give Buck his second wicket.
But the Bears rebuilt well after that, with Colin de Grandhomme and Woakes playing some big shots and the Steelbacks' fielding starting to let them down a little.
A couple of dropped catches were looking likely to be costly as the Bears reached 120 for four with five overs to go, but de Grandhomme was then trapped LBW by Prasanna for 12.
Woakes was looking in fine form though, having been handed a Test call for England's clash with India, which starts on Thursday, earlier in the day.
He did some damage to Gleeson's figures in the bowler's final over as frustration started to grow in the stands.
But Elliott was to go for 19 as the Bears skipper top edged to Charlie Thurston off the bowling of Hutton.
Woakes was in fantastic form and he reached his half-century from just 22 balls in the final over as the Bears finished with a flourish.
Aaron Thomason was run out from the final ball of the innings for three, but the Bears had climbed up to 187 for seven.
And they were to strike early in the Steelbacks innings, with former Northants pace ace Olly Stone bowling Duckett for just two in the third over.
But Cobb came in and put the pressure on the bowling side, racking up 21 runs in the powerplay as the Steelbacks ended it on 45 for one.
Ricardo Vasconcelos went in the next over, which was bowled by Elliott, as Thomason took a superb catch on the boundary to dismiss the Steelbacks opener for 18.
Alex Wakely was next to go, for seven, as he was caught by Hose on the boundary, giving Elliott a second wicket to leave the Steelbacks on 72 for three in the ninth over.
Cobb continued to counter well though, reaching his 50 from 35 balls.
But after he ran a single, Thurston was dismissed next ball, with Stone taking the catch at backward point.
Cobb was refusing to give up the fight and he took Woakes to task in the 13th over as the Steelbacks remained ahead of where the Bears were at the same stage.
But no one was sticking around at the other end as Steven Crook became the latest batsman to fall cheaply, going for three as Hain took the catch off Patel.
Prasanna could only make five before top edging one off Elliott, leaving a simple catch for wicketkeeper Tim Ambrose.
At 118 for six and with only bowlers left to join Cobb in the middle, the Steelbacks were really struggling.
Hutton held up one end while Cobb reached a fantastic century, drawing a standing ovation from the home fans.
But it was in vain as the Bears got the job done in the final over, with Cobb run out for 103 and the Steelbacks finishing on 170 for seven.
Steelbacks: Vasconcelos, Duckett (wk), Cobb, Wakely (c), Crook, Thurston, Prasanna, Hutton, Buck, Gleeson, Sanderson.
Birmingham Bears: Pollock, Bell, Hose, Hain, De Grandhomme, Elliott (c), Woakes, Thomason, Ambrose (wk), Patel, Stone.