Some sloppy play at both ends of the pitch cost Pompey at Scunthorpe.
Poor defending allowed Lee Novak and Duane Holmes to give the Iron a commanding lead at the interval.
But the visitors missed opportunities – most notably an Oliver Hawkins header from close-range – and were frustrated by a well-oiled rearguard display.
And while Jackett praised their opponents’ defending, he knows his side have to be sharper in front of goal.
The Blues boss said: “Scunthorpe got their noses in front during a key period when it was end-to-end and two mistakes from our point of view let them in.
“After that it was very difficult for us to break them down. They were very happy for us to have the ball, but we couldn’t penetrate.
"They were very happy for us to have the ball, but we couldn’t penetrate."
“We couldn’t find the right ball at the right time and when we got the ball into their box, it was always a Scunthorpe head on the end of it.
“Hawkins had three back-post headers and he’s either got to get them back across goal or get the ball on target.
“I just felt that they did a job on us and the game petered out. They’d only conceded eight goals and it showed why.
“We haven’t scored enough from corners and free-kicks this season and in tight games like these, you need to take those chances.
“One set-piece can get you back in the game and provide some confidence, so that’s something for us to work on.”
A poor headed clearance by Dion Donohue led to Scunthorpe’s second goal, but Jackett was happy with the left-back’s contribution.
He said: “Dion generally played well, but just made one or two mistakes in an otherwise positive performance.
“He did a lot of things very well for us and has a nice left-foot, delivering well from set-pieces.
“There are a lot pluses for him and it’s still early in his Pompey career, but eradicating those mistakes will be top of his list.”