Steve Evans believes Mansfield deserved a win against Pompey but squandered too many chances.
And he was adamant Matt Clarke should have been sent for an early bath.
The Blues earned a hard-fought 1-0 win at Field Mill, courtesy of Carl Baker’s strike in the 56th minute.
The hosts had the majority of the better chances, however, with Shaq Coulthirst chipping his effort over David Forde when left one-on-one when the Stags were 1-0 down.
Mansfield also had claims for Clarke to be sent off when the game was level, after tripping up Danny Rose when he was through on goal.
Defeat for the Stags, who dropped to 12th in the League Two table, means they now face a mammoth task of securing one of the play-off places.
But Evans reckons his side were unlucky losers and criticised referee Lee Swabey’s performance.
He told the Hucknall Dispatch: ‘There were two outstanding teams out there.
‘We were the better team on the day, but we lost.
‘I have to be careful what I say, but that was an atrocious refereeing performance.
‘You always look at reactions and I look at their centre-half throwing his hands on his head – he thought he was away and so did their bench.
‘The Portsmouth staff are feeling for us. We all know what would have happened if that had been us at Fratton Park, and it had happened in reverse.
‘I don’t think the referee would have been allowed to leave Portsmouth.
‘Paul Cook said to me at the end that was the worst decision he’d seen in his career and I think I join him.
‘But I think we all know if we’d had a goalscorer when we walked into the football club we’d be up automatic, not worrying about the play-offs.’
‘My players gave everything and they were bemused.
‘It’s not often you see a full dressing room just struggling to accept what’s happened.’
– WILL ROONEY