Steve Cotterill felt the dismissal of Liam Lawrence was the key moment as Pompey went down 4-3 at West Ham.
The Blues skipper was given his marching orders with the game on a knife-edge at 2-2 after he collected a second yellow card for a late challenge on David Bentley, having already been booked for a tackle on Henri Lansbury.
While Cotterill had no complaints over the second yellow card, he took issue with the first decision by the referee that led to Lawrence’s red card.
Cotterill said: ‘The sending off was the turning point. I think we were the better side.
‘We came to a great club like West Ham with a full house and I thought we played our football.
‘We were very, very unfortunate to not get three points. I thought we were really good.
‘I don’t think the first booking for Liam should have been given for the sending off. The refeee was pernickety all afternoon.
‘There were a few bookings that shouldn’t have been given. But that’s the way it went this time.’