Pompey are preparing to face a 15-year-old powerhouse at Pride Park tomorrow.
Mason Bennett became Derby’s youngest ever player after making his debut in the 2-0 loss at Middlesbrough last weekend.
The stocky striker is expected to keep his place after he impressed at the Riverside and scored twice for England under-16s against Northern Ireland recently.
Bennett was handed his opportunity by Rams boss Nigel Clough with forwards Steven Davies and Nathan Tyson both out injured and strike partner Theo Robinson felt he had shown maturity beyond his years.
Robinson said: ‘Mason played well at Middlesbrough.
‘Even at 15, he was bullying defenders, which is a good sign.
‘I spoke to Mason before the kick-off and just told him to enjoy it.
‘I told him he was the best player in the England under-16 game the previous week, so just do what he did that night.
‘Hopefully he can do that against Portsmouth.’
But Pompey joint caretaker boss Guy Whittingham is aware of Derby’s new weapon.
He said: ‘I was still at school probably playing for the local team when I was 15. It shows the promise he has.
‘I’m sure he wouldn’t be involved unless Nigel Clough thought he was good enough.
‘They’ve obviously got a promising kid there and it shows what a good youth system they have.’