Pompey travelled to Shrewsbury having won seven of their previous eight matches.
So the hope was that they would be driving home for Christmas with another three points in the bag.
The high-flying Shrews had other ideas, however, and a 2-0 victory strengthened their automatic promotion credentials.
Luke McGee saved a penalty before goals from Shaun Whalley and Stefan Payne ensured the hosts came out on top.
And Kenny Jackett conceded that his side did not do enough to get anything from the New Meadow contest.
The Blues boss said: “It hurts me to say it, but Shrewsbury were better than us. They were relentless and deserved to win.
“They closed down very quickly and we couldn’t get any momentum on the ball, while the second goal really typified the way the game went.
"We just didn’t do enough to hurt Shrewsbury and I believe that was our Achilles heel."
“We couldn’t find a player who could beat his man in possession or a passage of play and we couldn’t get in behind them.
“In the first half we did okay defensively, but need to do more going forward and be more constructive with the ball.
“We just didn’t do enough to hurt Shrewsbury and I believe that was our Achilles heel on this occasion.
“We won’t beat ourselves up, but have to be honest and work out how to be better and get into their position.”
An error from McGee led to Shrewsbury’s opening goal, while Matt Clarke was at fault for the second.
Jackett said: “You wonder whether the penalty save is going to change things, but then Luke made a mistake for the first goal.
“He’s been a good player for us, though, and we can’t look at this result and say it was down to one individual.
“It’s the same with Clarkey for the second goal because we weren’t brave enough as a side and there weren’t enough chances."