Swindon boss Paolo Di Canio called on his side to "become a nasty team" after they clung on for a 2-1 victory at Portsmouth on Tuesday.
The Robins dominated the south coast outfit for the first 80 minutes, taking charge through goals from Matt Ritchie and Andy Williams, but Pompey laid siege to the Robins goal late on with Lubomir Michalik heading in two minutes into stoppage time in League One.
Di Canio said: "I learnt that we are not ready yet for the top of the league. This is a different level. If you switch off for eight minutes, you can concede five goals to the opponent.
"We played 80 minutes where we should have been 10 or 12 goals up. We didn't take all the chances; it's not possible every time. But we then switched off a bit and the opponent created four or five clear chances.
"We have to grow up like we did last year and realise we have to work, analyse the last 10 minutes and become a nasty team, a malicious team in every situation.
"Portsmouth didn't become Barcelona in the last 10 minutes - we put the result at risk. I am not happy."