Danny Rose has called on Pompey to swiftly adapt to their League One surroundings if they are to flourish.
A below-par Blues suffered their first defeat of the league campaign on Saturday.
In this league, mistakes get punished a lot quicker and that is something we have to be more aware ofDanny Rose
Oxford United netted three times in the second half of their Kassam Stadium clash to claim a fully-deserved 3-0 victory.
A lacklustre Pompey struggled to threaten in the final third of the pitch as the U’s bossed possession for long periods.
Pep Clotet’s side looked every inch a team which last season finished eighth under previous boss Michael Appleton.
Certainly lessons require learning by Pompey having returned to League One after four seasons away.
And Rose believes the players must quickly come to terms with what’s required in their new surroundings.
He said: ‘You can’t forget how well Oxford did last year.
‘Playing against them during the middle of the game, we knew we were going toe-to-toe against them and couldn’t hold our own.
‘Unfortunately their quality came through in terms of the second goal – which the lad took really, really well – and we tried to push again hoping to get a couple more, but it wasn’t to be.
‘In this league, mistakes get punished a lot quicker and that is something we have to be more aware of.
‘That is the case of any level, the higher you go the more chances the strikers will take.
‘That is probably the main thing I have noticed so far.
‘By and large the game is probably quicker in general – but at the top end of the pitch strikers take their chances.’
For Rose himself it was only a second League One outing in his career.
Like many of his team-mates, the 29-year-old possesses an inexperience at the level Pompey find themselves in.
Still, the disappointing scoreline came on the back of an encouraging display at Championship side Cardiff in the Carabao Cup in the week.
That gruelling match ran into extra-time during a gutsy display from Kenny Jackett’s team during a 2-1 loss.
Rose admitted the Blues’ endeavours may have had an impact on Saturday’s performance against the U’s.
But he refused to use it as an excuse behind their poor showing against a team which also lost after extra-time.
He added: ‘Maybe Cardiff affected us in the legs, but that’s no excuse.
‘Oxford had extra time as well (against Cheltenham) so I don’t think that makes any difference on the result.
‘In the first half we contained them and the threat they possessed, the game was pretty even really.
‘I think we probably created the better opportunities in that period and were looking forward to the second half and getting back out there to get a result.
‘But we gave ourselves too much work to do in the end and lost.’