Pompey were dominant in possession and looking comfortable at the Stadium of Light.
Unfortunately, they were unable to convert that control into a goal and were made to pay against title-chasing Sunderland.
Elliot Embleton stole possession and played a neat one-two with Ross Stewart before slotting home the game’s only goal.
And Danny Cowley was annoyed to see his side once again be undone by their failure in the final third.
The Blues boss said: “We’re frustrated not to take something from the match and I can’t fault the effort or attitude of the players.
“At the end of a three-game week, Sunderland is probably the toughest place to come and we gave it our all, but we probably fell a bit short.
“We had a really good start and were in total control for the first 30 minutes, with a rhythm and tempo to our performance.
“There were some chances created and we really need to take them when we’re on top. We need that quality in the final third.
"When you do go 1-0 down, the onus is on you to build and create, but it was hard to get ball speed and break down a good side."
“It was a difficult pitch to play on – certainly not one befitting of such a great stadium and football club.
“When you do go 1-0 down, the onus is on you to build and create, but it was hard to get ball speed and break down a good side.
“But we became too risk-averse and were too direct, not winning the second balls. We lost some control.
“Michael Jacobs came on and provided some quality that we’d perhaps been lacking. He’s trained well and affected things.
“My initial feeling afterwards is that we definitely played well enough to have taken something from the game.
“We know the areas we’ve been short on lately and it’s not for the want of trying, but we have to keep working on it.
“There are good players here and sometimes it’s down to confidence. Our performances this past week have deserved more, but the only stat that counts is the scoreline.
“I want to thank the supporters, who were tucked away up in the gods. It’s an incredible journey to make and I wish we could have given them something to celebrate.”