Mikey Harris believed Pompey’s fitness and extra quality was decisive as they claimed a late FA Youth Cup win over Metropolitan Police.
It took Matt Mayes’ 80th minute header for the Blues’ youngsters to finally break the deadlock.
Tommy Scutt sealed the 2-0 Fratton Park victory in stoppage time to see off the hard-working non-league club.
Pompey’s Academy had to be patient to secure the win which has earned them a third-round clash with Newcastle.
Yet coach Harris insists he was always confident they would find the breakthrough to end The Met’s resilience.
He said: ‘You have got to be patient at times, you don’t have to score in the first half to win a game, you don’t have to score in the first 80 minutes to win a game.
‘You just need to make sure you get those goals at the crucial times.
‘We always believed we had a goal in us, it’s very rare when we’ve not scored and I was always confident – even going into the final 10 minutes – we would get that goal.
‘The Met had given everything to be fair to them and were starting to fatigue, you could see that from the side of the pitch.
‘Massive credit to them, they gave absolutely everything, but in the end it was our fitness and that little bit of quality which told.’
In a match of few goal-scoring opportunities, as the fixture wore on it appeared extra-time may be required.
The Met had their moments, though, Jamie Autorino’s viciously in-swinging second-half corner touched onto the far post by Nick Hall.
The keeper had also pulled off a stunning stop to deny the same player during the first half.
However, Pompey always looked the most likely to score and, on 80 minutes, McDowell’s cross from the left was headed home by Mayes.
The scoreline was increased one minute into stoppage time as Scutt tucked home Jez Bedford’s pass.
During a strong finish, there could have been more goals, yet the Blues had enough to see off the visitors.
Harris added: ‘It wasn’t dissimilar to a lot of the first-team games we’ve seen at Fratton Park this season, with sides coming to frustrate and stay in the game as long as possible, nicking a goal on the counter attack.
‘The Met posed a threat on the counter all night, they had pace in wide areas and up top and we had to concentrate throughout.
‘We had to stick to the gameplan, which was to try to retain possession, try to open them up, attempt to get down the sides and get deliveries into the box.
‘We put 41 crosses into the box and if you do that you hope to create chances.
‘It took a bit of time, but Kyle McDowell put in a great delivery and Matt was in the right position to head it home.
‘Then Jez Bedford did the right thing to set up Tommy. Now we can look forward to Newcastle.’