It was an extremely rare off night for the Blues on their League One travels this season.
Blackpool had previously been the only team to send them home empty-handed, but Bristol Rovers joined the list.
John Marquis had opened the scoring for the visitors, only for some sloppy play to ensure the Pirated ended up with a 3-1 victory.
Jonah Ayunga took advantage by bagging a brace, while Luke Leahy added another goal from the spot after being fouled by Sean Raggett.
Marquis then missed a stoppage-time time penalty, leaving Joe Gallen to reflect on a disappointing display.
Pompey’s assistant manager said: “Our away form this season has been very good and we’ve had some excellent results on the road.
“It’s unlike us to concede that many goals in a match and it’s given us a lot to do. That’s why we’ve ended up with nothing.
"It’s difficult to criticise any players, though – particularly the defenders – because they’ve performed very well this season."
“Their two forwards played in a direct way and it’s caused us a lot of problems in the first half, while the third goal is a mistake and it’s taken the game away from us.
“It’s difficult to criticise any players, though – particularly the defenders – because they’ve performed very well this season.
“We’ve kept plenty of clean sheets and have won a lot of games because we’ve managed to keep the scoring down for our opponents.
“Sean is having an outstanding season – there aren’t too many centre-backs better than him in this division.
“He’ll knows that he’s made an error, but he’s got plenty of character and I know he’ll bounce back from that.”
Blues boss Kenny Jackett took in the match from home as he prepares for a operation later this week.
Gallen said: “Kenny watched the game on iFollow and I was in regular contact with him about the changes, the shape and any decisions that needed to be made.”