The former Blues assistant manager was left floored after his team gave up a two-goal half time lead and fell to a 3-2 reverse at Fratton Park last night.
That meant the Latics’ League One promotion and title hopes faltered and now will go to the final day.
Pompey were much the better team in the first half of crackling encounter, but didn’t create enough for their pressure.
They were then undone by a couple of clinical attacks from the visitors as Callum Lang and Will Keane snaffled away opportunities.
Two goals from George Hirst in two second-half minutes changed the face of the game, however, before Aiden O’Brien won the match with three minutes remaining.
Richardson felt there was a debate about whether Marcus Harness fouled Tom Pearce, as he turned the ball over for Hirst’s first goal.
But he had no complaints that the team who showed the greater attacking intent emerged victorious on the night.
He said: ‘I'm obviously very disappointed with the manner of the result.
‘But on the balance of the game they were just a bit better than us offensively on the night.
‘I thought we defended resolutely and well until the first goal and then you'll debate the three goals.
‘Whether there should have been a free-kick to us - and they played on.
‘The second goal is obviously a mistake and the third’s a set-piece.
‘It's still all in our hands, we've worked tirelessly hard and nothing changes.
‘Every single team in the league would swap places with us now, it's that challenging.
‘Campaigns don’t change, it’s 46 games.
‘It's just important to stay realistic, and this group of players has done consistently well for us all year.
‘The habits will be the same at the weekend as they have been all year.
‘And if you work hard and keep your standards high, you'll normally get the results you deserve.
‘There’s a good team here and if we can keep players next season looks good.
‘It’s important I and the senior players lead.
‘When you’ve been in these campaigns you know what it takes.
‘We firmly believe with more work ethic we’ll end up where we deserve to be.’