The Saints stormed to a 21-0 half-time lead at Rodney Parade with three first half scores – while Dragons were reduced to 13 men at one point.
The home side rallied with Elliiot Dee and Jarryd Sage scoring - plus a late penalty try with the final play of the night - but they were left empty-handed after an error strewn opening 40 minutes.
“We are really frustrated with our first half performance,” said Jackman.
“We knew, having scouted Northampton, that you can’t give them set piece opportunities in your own 22. But, from the very start, we made errors.
“We gave them momentum, didn’t deal with a high ball twice and then gave away a soft penalty that led to them scoring the opening try.
“We backed it up with a defensive error for an easy try from their own half.
“Then we give away a scrum penalty on our ball and that led to two boys being sin binned.
“You can’t give these big English teams that many set piece opportunities. It was a harsh lesson for us to learn tonight.
“I thought the boys managed the last period with 13 men well, dug in for each other and when we got back to 15 we went at them and played some good rugby.
“But when you are chasing the game like that they only need one breakaway score and you lose your chance.”
Dragons scored three second half tries, but Jackman insisted they should have taken at least a try bonus from the match.
“We should have gone on and got the four try bonus in the second half with the way the game went, but mistakes cost us. Collectively we didn’t nail the big opportunities,” added Jackman, who revealed later that Jared Rosser had suffered a hamstring injury.
“The only pleasing thing was that the boys showed real heart and courage in the second half. But we’ve got to fix the technical and tactical issues that let us down.
“It’s going to be tough now,” he admitted. “We need to beat Clermont at home and go to Saints – we have made it hard for ourselves.
“We need to get smart quick. It’s those metal errors that you can’t afford to give and the sooner our players realise the higher the concentration levels the easier games will be. At the moment we are making it hard for ourselves.”
