Simon Bassey rued a lack of clinical edge as Pompey exited the Papa Johns Trophy at Bolton.
Jón Dadi Bödvarsson struck in the first half to ensure it was the home side who progressed to the semi-finals.
There were plenty of moments when the Blues found themselves in promising situations in the opposition half.
But that failed to convert into many meaningful chances and Bassey wanted to see more attacking quality.
Pompey’s interim head coach said: “We weren’t aggressive enough in the first half and lost too many duels – ultimately we’ve conceded a really poor goal.
“It was a good situation for us, but the counter-attack hasn’t been defended properly and it’s cost us in this instance.
"You need to work on that mental side because for the best players, the game slows down when they get the ball on the edge of the penalty box."
“We turned the ball over four or five times, but lacked the quality and decision making to find that killer pass.
“I thought we addressed that at the break and were the better team in the second half, but were left chasing it.
“We got into some good areas, but were again missing that detail in our passing to really find those scoring opportunities.
“It’s an area that we certainly need to improve on because the boys are looking a bit anxious in the final third.
“You need to work on that mental side because for the best players, the game slows down when they get the ball on the edge of the penalty box.
“There’s a lot of attacking talent in our squad, but they have to produce in those moments because that’s what they’re paid to do.”