The black, green and gold scored six tries in a dazzling display at the Brentford Community Stadium.
They spoiled the home side's St Patrick's Day party and moved above Irish in the Gallagher Premiership standings in the process.
And Irish boss Kidney was not happy with the amount of chances his side gave to Saints.
"There was a period in the first half where we gave Northampton confidence because we stopped playing," said Kidney, who had seen Irish move into an early 8-0 lead.
"They picked up 14 points and then we made the third quarter very difficult for ourselves again.
"The scoreline doesn't concern me and we can turn that around but it's just that period in the first half where we let them back into the game.
"We'll have to look back at it.
"We made a strong start and there were times we had people in the clear so we were creating the chances.
"If we weren't creating the chances I would be more worried, but we did that.
"If you give a good side like Northampton as much of the ball as we did, they're going to take their opportunities.
"They got momentum, they got scores during the sin-binnings and that's what good sides do.
"We knew Northampton would be better with their internationals back and they played a good game, but there's a lot of it we can control and those are the areas we'll have to look at."