Blues boss Guy Whittingham believes John Sullivan is starting to show his first-team worth.
The keeper was a furious figure at the final whistle against Burton on Saturday after his prized clean sheet was snatched away at the death.
Zander Diamond’s goal in the fifth minute of time added on was a painful blow for the keeper.
But it did not cost Pompey a 2-1 victory at the Pirelli Stadium.
It was Sullivan’s fourth appearance in succession, having won the shirt back off Phil Smith.
The 25-year-old turned in an assured display.
His handling, kicking and command of his area were faultless during the 90 minutes.
Whittingham is pleased with the way the summer recruit is progressing.
He said: ‘John has the shirt now, absolutely.
‘He wanted to come here at the start of the season and establish himself at number one and he is doing it.
‘As a goalkeeper and defence you pride yourself on clean sheets – and I do feel disappointed for him because, again, he’s had a decent game.
‘Against Burton his kicking was great. I thought he came and got some good crosses and, from that point of view, defensively I was very pleased.
‘I think John has got the bit between the teeth.
‘He realises he is establishing himself as number one and that is what he needs to do.
‘That is down to hard work on the training pitch, concentrating on things when you are doing them – and I cannot remember the last time he mis-kicked a ball.
‘Defensively, Burton was our best game of the season.
‘You can’t rely on keepers to pull you out of the mire every single time so the defence was strong and the goalkeeper was strong.
‘Confidence is the biggest asset to any player in any team, no matter what position you play.
‘I think over the last two or three games John’s has been growing.’
The battle for the jersey has sparked much debate early in the campaign.
Sullivan started as number one, then Smith took over in goal for four matches.
The former Charlton man took back his spot after Smith’s Mansfield mistake.
The Blues continued to be linked with keepers but Whittingham insists he is not going to bring in anyone ‘at the moment’.
‘We are not looking to get any keepers in at the moment,’ said Whittingham.
‘But I am always looking to get players in, in every position, in case something happens.
‘As we have seen with Joe Devera, he has a hamstring strain now so that leaves us with two centre-halves.
‘If one of the goalkeepers go down we have to act quickly.
‘So we have always got our eye on who is around and who is not around.
‘We wouldn’t be doing our job if we didn’t.’