Guy Whittingham has admitted he still remains unsure who his number one Pompey keeper is.
The Blues boss dropped Phil Smith and restored John Sullivan to the starting line-up on Saturday for the visit of Chesterfield.
Regardless, 10-man Pompey slipped to a 2-0 defeat as the visitors netted two goals in the final three minutes.
Armand Gnanduillet’s powerful 87th-minute header gave Sullivan no chance, while Tendayi Darikwa’s deflected angled drive sealed the victory.
For the ex-Charlton keeper, it was a first appearance since being left out following the opening-day defeat to Oxford.
Smith had taken over in the subsequent four matches, although his clanger robbed Pompey of a win at Mansfield in the previous match.
Whittingham has revealed Sullivan will retain his place for tomorrow’s Johnstone’s Paint Trophy trip to Torquay.
But he is still undecided which of the pair is going to be his undisputed first choice.
He said: ‘I know one of them is going to step up to be number one but I have to give both of them the same chance to do that.
‘I have not decided who is my number one, though.
‘What I do believe is one of them will establish themselves as a keeper here for the rest of the season and John has his chance now and he needs to take it.
‘Unless it’s a massive mistake then he can look forward to a run in the team.
‘Last time in a cup game I did change it but that was pre-planned.
‘Not this time, so he will also start tomorrow.
‘I think John did well on Saturday, he came and collected a couple of balls well and his kicking was decent enough most of the time.
‘You look at the game and you always look at conceding and how you could have done better.
‘For the first goal it was probably the first header Sonny Bradley didn’t win all match.
‘But Gnanduillet is a big lad to come on. He had fresh legs and it was a good cross and a great finish from him.
‘For the second we have gone three at the back, so that is why the guy (Darikwa) had a bit more space than he would have done.
‘We’ve put Tom Craddock on and if we had stayed the same then he wouldn’t have had the space because Danny East would have been back there as well – then it has taken a deflection and gone past John.’
Definitely not featuring at Torquay will be David Connolly as he starts a three-match ban.
His straight red card in the 38th minute following an off-the-ball clash with Sam Hird proved to be a game-changer.
But Whittingham wants to assess the footage before taking any possible action against his skipper.
He added: ‘I didn’t see it and haven’t spoken to him yet.
‘Our players said he (Hird) had an elbow in the back and has gone down but David knows better.
‘We will look at the incident because ultimately we have gone down to 10 men in a game that if we had 11 men I would have liked to think we could have come out with at least a point.
‘But I’d rather reflect on those on the pitch and what they did well.’