David Ripley reflected on a 'bad night' for his Steelbacks side after they were thrashed by 48 runs at home to Leicestershire Foxes.
The Foxes racked up 193 for five before restricting Ripley's men to a tame 145 for seven, in which they lost five wickets for just eight runs.
It was Leicestershire's first T20 win against Northants since 2011 and tough for the Steelbacks to take.
The champions had won their previous two NatWest T20 Blast games and were second in the North Group going into the County Ground clash.
They remain second, but know their buffer has gone and they must do the business at Yorkshire Vikings on Thursday and at home to Durham Jets next Friday.
"It's just a bad night - we didn't play well," Ripley said.
"Over 14 games, you have a night generally where you don't play well and that was it.
"We can't afford another one because it's going to be tight going into the last two games next week, but if you go through 14 games in T20 cricket and don't have a bad night you'll have done well.
"We're disappointed with the size of the defeat and it will affect our net run rate as well.
"We went for too many sixes, we gave them chances to hit with the wind to the short boundary and get underneath the ball.
"There were 10 sixes for them and only two for us and that's quite a big swing.
"Adam Rossington (who hit 67) kind of fought a lone battle, but at the halfway stage I still thought we had a chance.
"Adam and Alex (Wakely) had got us ahead on the Duckworth-Lewis route, but we just fell away so quickly.
"We were perhaps a little short of batting without (Josh) Cobb and (Seekkuge) Prasanna so it was tough for us to get up to 190."