Kenny Jackett felt there was a ‘clear push in the back’ on John Marquis that earned Pompey a penalty at Bristol Rovers.
The Blues were given a golden chance to break the deadlock in the ninth minute of the trip to the Memorial Stadium on Saturday.
Marquis received a nudge in the back from Luke Leahy when trying to get on the end of a bouncing ball, with referee Darren Hanley immediately pointing to the spot.
Jackett, however, believes the official was correct.
The Pompey manager said: ‘I thought it was a clear push in the back and it was a penalty.
‘I’ve looked at it again, I’ve looked at all the incidents because it was a key incident.
‘There was a push in the back, the appeal was there and the referee has given it.’
Pompey had opportunities to double their advantage before half-time but home keeper Anssi Jaakola made several fine saves.
He kept out headers from Christian Burgess and Sean Raggett in quick succession, as well as holding onto a Marquis shot.
The Blues did double their advantage on 70 minutes through Ronan Curtis’ firm header.
But despite being in full control, Jackett’s side would return to the south coast with just a point.
Alex Rodman reduced the deficit with 12 minutes remaining before a stoppage-time own goal – which went down as Craig MacGillivray’s – meant Pompey had to settle for a draw.
Despite the Blues missing a number of chances, Jackett didn’t feel they cost his side.
He added: ‘To be fair, the keeper pulled off some great saves – that’s what the keeper is there for.
‘They’re big chances but we didn’t do a lot wrong in terms of misses.
‘We got them down, got them on target but the keeper picked off those ones.
‘Having said that, we still went from 1-0 to 2-0 and it's not like it necessarily cost us.
‘The end bit is very frustrating for us all.’