Andy Awford urged his academy heroes to remain grounded after pulling off a stunning victory over Southampton.
Heading into Saturday’s clash, Pompey were 15 points adrift at the bottom of the Premier Academy League group A table.
In contrast, their fierce local rivals topped the crop ahead of Crystal Palace.
Yet Awford’s youngsters claimed a shock 2-1 win at the Wellington Sports Ground, despite Sam Hoskins giving Southampton a first-half lead.
An Ashley Harris free-kick and then a Ryan Williams strike 10 minutes from time secured a memorable triumph which was only Pompey’s second win in the league this season.
Awford has only been academy manager for three weeks, replacing Paul Smalley.
But he is keen to stress the importance of not getting carried away and focusing on the bigger picture.
He said: ‘Hopefully the win can give the lads the self-belief and confidence which has been lacking at times.
‘We actually didn’t start that well for 20 minutes.
‘We were second best and Southampton deservedly took the lead after about 25 minutes.
‘They also hit the post but Ashley Harris scored a wonderful free-kick to get us back into it after 35 minutes.
‘From that moment, the lads got that bit of belief and thought they could get something and we were the better team in the second half.
‘Then, 10 minutes from time, Carl Walshe – who had worked hard up front – managed to stick a decent ball into the box and Ryan Williams finished it nicely.
‘I’m delighted for them but this is very much a starting point, we need to build on that.
‘At the end of the game, a couple of people were jumping up and down as if they’d won the World Cup.
‘I don’t want to take anything from them, enjoy that moment.
‘But we have got to work as hard this week as last week.
‘If they don’t, they will get nothing in our next match against Charlton.
‘They have got to come back in today and go to work and start from scratch.
‘You have to do things properly and gradually – we want to make sure that is the case.’
Pompey: Gledhill, Tallack, Magri, Tsovolos, Grant, Seeley (Jennings, 56mins), Stockford, Harris, Butler, Walshe (Antelmi, 90mins), Williams. Subs not used: Fitzharris, Bennett, Vine