Graham Alexander felt Pompey changed their formation to nullify his team.
The Scunthorpe boss believes the Blues’ shift to wing-backs was all about negating the threat of his men.
Pompey had the better of a first half Alexander viewed as scrappy but he felt the Iron came to terms with what was needed as the game wore on.
He told scunthorpe-united.co.uk: ‘We more than held our own, once we realised what we needed to do in the game.
‘We had the best opportunity right at the start of the game but didn’t manage to take it.
‘They then scored from their first chance and the first half was a scrappy affair, with them changing their formation to combat ours and nullify us.’
Alexander explained he needed to change things tactically for Scunthorpe to get a foothold in the game.
He said: ‘We changed a couple of things at the break and the players realised how good a team they are – and as individuals.
‘We showed better composure in the second-half, we were more aggressive in our first contacts on the back four and did the basics right.
‘That’s what got us the initial foot down in the game and to be fair, we dominated the second-half, got an equaliser and pushed all out for the winning goal.’
Alexander was pleased with the game’s outcome as his men left Fratton Park with a point.
He said: ‘We had to be respectful and wary of the threat Portsmouth pose because they have really good attacking players.
‘We did really well but it’s just disappointing we couldn’t find that second goal.
‘We reminded the players of the basics and added a bit of composure.
‘We were disappointed with the goal but they showed more confidence and we scored, we got on the front foot and dominated the second-half.
‘It is a difficult venue to play at but we’ve showed we can compete at any arena and take points.’