It was Pompey’s best move of the match and ended with the ball in the Oxford United net.
But Danny Rose branded the adjudged foul which cancelled out Brett Pitman’s header as ‘soft’.
I think it was a little bit soft – although there was a little bit of contactDanny Rose
The moment arrived on 42 minutes during a tight first half at the Kassam Stadium, with the scoreline goalless.
Brandon Haunstrup’s cross from the left was headed home by Pitman – only for the referee’s whistle to cut celebrations.
Match official Graham Salisbury believed the Blues skipper had fouled a U’s defender as he rose to head home.
The visitors went on to lose 3-0 during the second half as Oxford stepped up their performance to claim victory.
Manager Kenny Jackett afterwards claimed the goal should have stood – and Rose agreed.
The midfielder said: ‘I think the referee gave it that way because perhaps Brett nudged the defender, which I think was debatable.
‘He may have leant in with his arm but whether or not it was enough for a foul I am not too sure.
‘If it was at the other end of the pitch where there is no stand behind the goal, perhaps he may have given it.
‘I think it was a little bit soft – although there was a little bit of contact.
‘I had a decent view, I was arriving towards the edge of the box, if I remember rightly. There was contact between the two players but it was a little bit soft.
‘It was just before half-time, we got a foothold in the game for the last 10 to 15 minutes and moved the ball pretty well, getting players like Benno, Naismith, Pitman and Evo on the ball in some good areas.
‘If that goal had stood we would have gone in 1-0 up at the break to give us something to hold on to.’
Having been denied a lead at the break, Pompey found themselves behind two minutes into the second half.
Christian Ribeiro’s cross from the right was fumbled by Luke McGee and bundled over the line by Wes Thomas.
That was the crucial breakthrough for the U’s – and a below-par Pompey never looked capable of coming back.
Gloss was added to the victory in the final eight minutes through goals from Gino van Kessel and Josh Ruffels.
And Rose was disappointed with the second half.
He added: ‘Conceding so early in the second half is something we are really disappointed with.
‘We gave ourselves a lot of work to do. Then trying to push forward to get a second goal saw us concede two towards the end of the game.
‘Looking back I don’t think we deserved a win.’