Hayden Mullins insisted he was fouled in the game’s critical moment as Pompey fell to defeat at The Den.
Mullins was floored by Millwall striker Dany N’Guessan as he grabbed the only goal of the match to give his team victory.
The Blues midfielder insisted he was pushed as Liam Trotter headed Liam Feeney’s cross into N’Guessan’s path.
Referee Nigel Miller allowed the goal to stand, however, condemning Michael Appleton’s men to their first loss in five games.
Mullins, who delivered an effective performance in the middle of the park, felt hard done by that the goal was allowed to stand.
He said: ‘I definitely felt a push. He was the wrong side of me, I was going to clear the ball and I felt arms in my back. I felt the push.
‘Those decisions either go for or against you, and it didn’t go the way we felt it should have.
‘I feel a little aggrieved about it but we have to get on with it.
‘The fans were getting on his back because they felt he was giving us a lot.
‘Maybe that was why he felt he should let it go. That cost us.’
Pompey looked a good bet to continue their unbeaten run for long periods against Kenny Jackett’s side.
They failed to carve out much in the way of clear-cut opportunities but also restricted Millwall to just a couple of chances on their own patch.
Mullins believes the approach laid down by Appleton is working.
The 32-year-old insisted the players are buying into the way the team has been set up – in terms of both tactics and formation. He said: ‘I think everyone is happy how we are going at the moment.
‘We look more solid, more organised and more compact as a unit.
‘I think we are looking harder to beat.
‘All the boys are buying in to what the manager is trying to achieve.
‘The result didn’t go our way but, in terms of looking solid, I think we did well.
‘We are hard to beat and I thought we looked like the team more likely to nick it.
‘Chuck (Norris) likes getting forward and scoring goals as much as Kits does.
‘He likes that role and can help us out when we need an extra man in midfield.
‘It works both ways and is a good formation to play.
‘We are capable of getting results playing that way.
‘Erik (Huseklepp) is capable of beating players.
‘Liam (Lawrence) can be a threat on the other side with his crossing and Wardy has legs when he is out there.
‘There is emphasis on them but they are up for it.
‘If we can keep it solid down the middle and get it out to them and the front men we will create chances.’