Lubomir Michalik's silly second half challenge on Chris Porter in the box gifted Sheffield United the penalty that would condemn Portsmouth to yet another defeat at Bramall Lane.
Nick Blackman stepped up to score the spot kick after the Slovakian needlessly slid in on the Blades striker to undo Pompey's previous good work in the first half.
Indeed, the first half saw Akos Buzsaky come close with a superb long range dipping strike that hit the crossbar whilst Scott Allan impressed on his second debut for the club, highlighting his performance with a driving run up the pitch and past the United players only to drag his shot wide.
Izale McLeod also saw his strike fly over the bar from a tight angle as the Blues were comfortable after the first minute, when Blackman rushed through on goal but could only hit the feet of Mikkel Andersen with his strike.
Having been in control in the first half, Pompey struggled to maintain their dominance in the second as Danny Wilson's side upped their game and Harry Maguire came close with a volley near the corner of the box.
Pompey's influential men struggled to keep hold of the ball in the second half but it still seemed like a draw was on the cards until the moment of stupidity from Michalik.
Andersen didn't even move as Blackman coolly slotted the penalty into the back of the net and that was ultimately the end for Pompey who could not muster a decent chance after that and in the end, left Bramall Lane with nothing once again.
It's a shame, because I don't think we deserved to lose on balance of play, especially in the first half when Pompey were clearly the better side with Andersen a virtual spectator.
And whilst Pompey may have had no shots on target, there were some good opportunities created against one of the toughest teams to break down in League One.
However, once again the level of performance could not be sustained and the team were lacklustre in the second half for not the first time this season. Yet again, Appleton has waited too long to change the game when the opposition are on top.
Despite the gripes, we should have got a draw from this game ad I'm still confident that Pompey can survive in League One as the performances are much better than earlier in the season, despite the results.
But next up is the first round of the FA Cup. It'll be interesting to see how many fans embrace the competition that Portsmouth won over four years ago now.
A performance similar to what we saw in the first half today sustained for 90 minutes should see Pompey progress to the second round where hopefully a more inspiring draw awaits.
Pompey Player Ratings
Mikkel Andersen: 6 - Little to do.
Mustapha Dumbuya: 5 - Delivery left a lot to be desired.
Gabor Gyepes: 6 - Comfortably dealt with most threats.
Lubomir Michalik: 5 - Solid until silly challenge.
Carl Dickinson: 6 - Looks to be at his level now.
Jon Harley: 6 - Industrious if wound up a little easily.
Lee Williamson: 6 - Unspectacular but not truly woeful against his former club.
Johnny Ertl: 5 - Seemed to go missing in the second half.
Akos Buzsaky: 7 - Bright spark that faded gradually.
Scott Allan: 7 - A real livewire, should give defences at this level nightmares.
Izale McLeod: 6 - Worked hard but not very threatening.
Substitutes
Simon Eastwood
Josh Thompson
Adam Webster
Liam Walker
Jack Compton
Ashley Harris (Harley 74): N/A - No impact.
Luke Rodgers (Ertl 78): N/A - Should have been introduced earlier, perhaps?